Acta Biomaterialia 9 (2013) 7093–7114

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Acta Biomaterialia

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Review Recent advances on the development of wound dressings for diabetic foot ulcer treatment—A review ⇑ ⇑ Liane I.F. Moura a,b, Ana M.A. Dias b, Eugénia Carvalho a,c, , Hermínio C. de Sousa b, a Center for Neuroscience and Cell Biology, University of Coimbra, 3004-517 Coimbra, Portugal b CIEPQPF, Chemical Engineering Department, FCTUC, University of Coimbra, Rua Sílvio Lima, Pólo II – Pinhal de Marrocos, 3030-790 Coimbra, Portugal c APDP, The Portuguese Diabetes Association, Rua do Salitre, No. 118-120, 1250-203 Lisboa, Portugal article info abstract

Article history: Diabetic foot ulcers (DFUs) are a chronic, non-healing complication of diabetes that lead to high hospital Received 14 November 2012 costs and, in extreme cases, to amputation. Diabetic neuropathy, peripheral vascular disease, abnormal Received in revised form 6 March 2013 cellular and cytokine/chemokine activity are among the main factors that hinder diabetic wound repair. Accepted 21 March 2013 DFUs represent a current and important challenge in the development of novel and efficient wound Available online 27 March 2013 dressings. In general, an ideal wound dressing should provide a moist wound environment, offer protec- tion from secondary infections, remove wound exudate and promote tissue regeneration. However, no Keywords: existing dressing fulfills all the requirements associated with DFU treatment and the choice of the correct Diabetes dressing depends on the wound type and stage, injury extension, patient condition and the tissues Diabetic foot ulcers Wound healing involved. Currently, there are different types of commercially available wound dressings that can be used Wound dressings for DFU treatment which differ on their application modes, materials, shape and on the methods Natural and synthetic polymers employed for production. Dressing materials can include natural, modified and synthetic polymers, as well as their mixtures or combinations, processed in the form of films, foams, hydrocolloids and hydro- gels. Moreover, wound dressings may be employed as medicated systems, through the delivery of healing enhancers and therapeutic substances (drugs, growth factors, peptides, stem cells and/or other bioactive substances). This work reviews the state of the art and the most recent advances in the development of wound dressings for DFU treatment. Special emphasis is given to systems employing new polymeric bio- materials, and to the latest and innovative therapeutic strategies and delivery approaches. Ó 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

1. Introduction type 1, type 2 and gestational diabetes. Type 1, insulin-dependent diabetes mellitus (IDDM), or juvenile-onset diabetes, is character- Diabetes mellitus is one of the most prevalent chronic diseases: ized by pancreatic b-cell destruction, leading to absolute insulin in 2010, it was estimated that 285 million adults worldwide had deficiency and, consequently, to the total dependence on exoge- diabetes and this figure is expected to rise to 439 million by nous insulin to sustain life [4,5]. The incidence of type 1 diabetes 2030 [1,2]. In North America and Europe, the number of adults is usually higher under the age of 15 though only 20-50% of pa- with diabetes is expected to increase by 42.4% and 20%, respec- tients are diagnosed before this age. In addition, the Caucasian tively, and a major burst in Africa is predicted, with the number population tends to present a higher risk for type 1 diabetes when of adults with diabetes expected to increase by 98.1% from 2010 compared to all other ethnic groups [6]. Type 2 diabetes mellitus, to 2030 [1,2] (Fig. 1). The main factors responsible for the increase also known as non-insulin-dependent diabetes mellitus (NIDDM), in the number of patients with diabetes are the growth and aging or adult-onset diabetes, is characterized by insulin resistance of the population and changes in lifestyle [1,3]. Diabetes mellitus is which may be combined with relatively reduced insulin secretion a metabolic disorder characterized by high levels of glucose in ser- levels. Type 2 diabetes affects approximately 90% of all diabetic pa- um and by changes in carbohydrate, lipid and protein metabolism tients and its main risk factors are high plasma glucose concentra- which are caused by alterations in insulin secretion, in insulin ac- tions in the fasting state and after an oral glucose load, being tion or in both of these processes [4]. Diabetes can be classified into overweight and a sedentary lifestyle [7]. However, this type of dia- betes can be delayed or prevented by a proper nutrition regime and by regular physical exercise [8,9]. Finally, gestational diabetes or ⇑ Corresponding authors. Address: Center for Neuroscience and Cell Biology, impaired glucose intolerance, which is first diagnosed during preg- University of Coimbra, 3004-517 Coimbra, Portugal (E. Carvalho). nancy, is defined as carbohydrate intolerance during gestation [10]. E-mail addresses: [email protected] (E. Carvalho), [email protected] (H.C. de Sousa). Gestational diabetes affects approximately 14% of pregnancies and

1742-7061/$ - see front matter Ó 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.actbio.2013.03.033 7094 L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114

Chronic diabetic neuropathy, defined as temporary or perma- nent nerve tissue damage, is a common complication of diabetes which is characterized by a progressive loss of peripheral nerve fi- bers that is caused by a decreased blood flow and high glycemic levels [29,44]. The duration and intensity of the exposure to hyper- glycemia strongly influences the severity of neuropathy [29]. Dia- betic neuropathy can be classified as peripheral, autonomic, proximal or focal, depending on the affected body part [45,46].It occurs in both type 1 and type 2 diabetes and is more frequent in older people. However, many diabetic patients may never devel- Fig. 1. Diabetes prevalence in the world, in 2010 and 2030 (adapted from Shaw op neuropathy while others may develop this condition rather et al. [1]). early [46,47]. On average, neuropathy symptoms begin to appear within 10–20 years of the diagnosis of diabetes, and approximately 50% of diabetic patients will develop nerve damage in some extent is also an important risk factor for type 2 diabetes in women [48]. [11,12]. Diabetic neuropathy and peripheral vascular disease are usually In addition and among other problems, diabetic patients are the major factors involved in DFUs. These two factors may act more likely to develop obesity [13–16], coronary heart disease, alone, together, or in combination with other conditions such as stroke [17–19], diabetic nephropathy [20–23], diabetic retinopathy microvascular disease, biomechanical abnormalities, limited joint [24–27] and diabetic neuropathy [28–31]. These diseases are lar- mobility and increased susceptibility to infection [48,49]. Some gely responsible for the observed high mortality rates in diabetic studies report that the difficulties associated with DFU healing patients. are mostly due to the excessive and persistent activity of metallo- proteinases (MMPs) and/or due to low levels of MMP inhibitors 2. Diabetic foot ulcers (DFUs) and impaired wound healing [50,51]. In addition, ischemia and vascular disease usually reduce the healing capacity due to the reduced supply of oxygen and Wound healing is a complex process that involves the simulta- nutrients to the wound area [52]. There are also impaired granulo- neous actuation of soluble mediators, blood cells, extracellular ma- cytic, chemotaxis and macrophage functions, as well as prolonged trix (ECM) and parenchymal cells. This process can be divided into inflammation and deregulation of the neovascularization phase several phases: homeostasis/coagulation, inflammation, prolifera- [53,54]. These issues are mainly due to impaired expression of tion (granulation tissue formation), re-epithelialization and growth and angiogenic factors, namely VEGF and PDGF [55]. Final- remodeling [32,33]. These phases are not typically associated with ly, there may be also nitric oxide abnormalities, collagen accumu- a rigorous and well-defined period of time and may overlap lation [56], abnormal migration and proliferation of fibroblasts and [30,34–36]. The transition between phases usually depends on of keratinocytes [55], as well as accumulation of ECM components the maturation and differentiation of keratinocytes, fibroblasts, and their remodeling by MMPs [57]. Fig. 2 schematizes the phases mast cells and macrophages which are the most important cells in- and growth factors involved in diabetic wound healing processes in volved in the wound healing process [37–39]. comparison with a regular wound. After tissue injury, a fibrin plug is formed in order to re-estab- In general, these chronic, non-healing neuropathic foot ulcers lish homeostasis, and aggregated platelets secrete several growth occur in around 15% of all the diabetic population [56] and are factors and cytokines (e.g. transforming growth factor beta (TGF- responsible for huge medical costs as well as significantly affecting b) and monocyte chemoattractant protein 1 (MCP-1)) that recruit patients’ quality of life [35,56,58]. Once a DFU has developed there neutrophils and monocytes to the wound site. These inflammatory is an increased risk of wound progression that may ultimately lead cells induce the expression of colony-stimulating factor 1 (CSF-1), to amputation (more than 85% of foot amputations in patients are tumor necrosis factor a (TNF-a) and platelet-derived growth factor caused by DFU) [49]. (PDGF) which are extremely important for the first phase of new The medical treatment of DFU remains a challenge. A better tissue formation process [40,41]. Re-epithelialization usually be- understanding of the pathophysiology and molecular biology of gins a few hours after injury. In response to these growth factors, diabetic wounds may help to find improved and more efficient keratinocytes and activated fibroblasts migrate from the wound solutions for their treatment. It is currently accepted that DFU edges into the wound site where they proliferate and construct therapies should be directed to actively promoting wound healing the ECM that will enhance wound closure [30,32]. The initial by correcting the expression of those biological factors which are ECM is gradually replaced by a collagenous matrix with the forma- important in the healing process [59]. Table 1 describes some of tion of new blood vessels (angiogenesis) [38]. The angiogenic fac- the most recent approaches that have been used to stimulate tors, such as fibroblast growth factor (FGF), vascular endothelial DFU healing. However, to date, their efficacies and/or their applica- growth factor (VEGF) and PDGF induce angiogenesis by stimulating tion mode have not been sufficient to guarantee adequate DFU the production of basic fibroblast and of vascular endothelial healing. growth factors by macrophages and endothelial cells [40,42]. Pro- Like for acute wounds, it is already well established that to en- tease expression and activity are also necessary for the angiogene- hance DFU healing processes, wounds should be dressed with ade- sis process [38,42]. When the wound area is completely filled with quate biomaterials in order to protect the long-term healing from new granulation tissue, angiogenesis stops and the apoptosis of contamination/infection, to prevent wound dissection (providing many new vessels is then started. The last phase of the wound an ideal moist environment to help wound closure) and, in the case healing process is characterized by the degradation of the previ- of medicated dressings, to provide a sustained and effective release ously formed granulation tissue and by dermis regeneration [39]. of the applied bioactive substances, as well as to prevent their ra- While acute wounds usually progress linearly through the different pid degradation during the healing process [60,61]. wound healing phases, the healing process in diabetic patients DFUs can be medically classified in a variety of ways but all of does not follow this timeline, but rather results in chronic non- them define the ulcer in terms of its depth and the presence of healing wounds that become stalled in one or more of the above- osteomyelitis or gangrene [62,63]. As an example, the classification mentioned healing phases [35,43]. according to Wagner’s system is based on the following grades: L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114 7095

Fig. 2. Differences in the normal and diabetic wound healing phases (adapted from Beanes et al. 2003). 7096

Table 1 Some different and recently proposed approaches to improve DFU treatment.

Bioactive Models used Results References substances Growth factors VEGF db/db diabetic mice Enhanced neovascularization, mobilization of bone marrow-derived cells into the Galiano et al, 2004 [257] wound site to accelerate wound healing PDGF STZ diabetic rats Enhanced angiogenesis, cell proliferation and epithelialization. Formed thicker and Li et al, 2008 [258] more highly organized collagen fiber deposition bFGF Human patients with DFUs Reduction of 75% of wound area in treated patients. Stimulated granulation and Uchi et al, 2009 [259] epithelization of tissues SDF-1 a STZ diabetic mice Increased EPC mobilization, homing and wound healing Gallagher et al, 2007 [260] Stem cells Bmscs STZ diabetic rats Promoted healing and improved the wound breaking strength. In addition, it Kwon et al, 2008 [261] increased collagen levels and TGF-b, KGF, EGF and VEGF expression CD133+ cells STZ diabetic rats Accelerated wound closure and promoted angiogenesis through stimulation of Barcelos et al, 2009 [262] endothelial cell proliferation and migration 7093–7114 (2013) 9 Biomaterialia Acta / al. et Moura L.I.F. Human adipose-derived stromal cells db/db diabetic mice Increased wound closure and stimulated production of extracellular matrix proteins Amos et al, 2010 [263] and secreted souble factors Embryonic stem cells STZ diabetic rats Reduced significantly wound size and increased expression of EGF and VEGF Lee et al, 2011 [264] EPCs db/db diabetic mice Promoted wound healing and vascularity and induced expression of VEGF and bFGF Asai et al, 2012 [265] Gene therapy Adenoviral PDGF-B db/db diabetic mice Significantly enhanced wound repair and neovascularization. In addition, adenoviral- Keswani et al, 2004 [266] PDGF-B stimulated EPC recruitment to the wound site Lentiviral-containing SDF-1 a STZ diabetic mice obese NOD/Ltj Improved diabetic wound healing with completely epithelialization and increased Badillo et al, 2007 [267] mice the granulation tissue Adenoviral-Hox B3 db/db diabetic mice Accelerated wound healing in diabetic mice Mohebali et al, 2008 [268] F-5 peptide (115-aa fragment of secreted db/db diabetic mice Promoted diabetic wound closure through the recruitment of both epidermal and Cheng et al, 2011 [269] Hsp90a) dermal cells and promoting dermal cell migration Proteins Substance P db/db diabetic mice Enhanced wound repair and increased early inflammatory density in the healing Gibran et al, 2002 [270]; wounds Scott et al, 2008 [271] Erythropoietin STZ diabetic rats Significantly reduced the time of total wound closure, increased micro vascular Hamed et al, 2010 [272] density, VEGF, and hydroxyproline contents and reduced extent of apoptosis Insulin STZ diabetic rats Enhanced wound healing and stimulated a faster epithelialization Apikiglu-Rabus et al, 2010 [273] Natural products Lithospermun erythrorhison extract db/db diabetic mice Decreased vascular permeability, formation of granulation tissue and accelerated Fujita et al, 2003 [274] wound healing Aqueous extract of Rosmarinus officinalis STZ diabetic rats Promoted ulcer healing accelerating the processes of tissue regeneration, Lau et al, 2009[275] (Rosemary) angiogenesis and inflammation Rehmanniae radix Alloxan diabetic mice Reduced inflammation and enhancement of wound contraction, re-epithelialization Abu-al-Basal et al., 2010 [276] and regeneration of granulation tissue, angiogenesis and collagen deposition in the treated wounds Ampucare (polyherbal ingredient) Alloxan diabetic rats Significantly reduced the wound size and bacterial count in wound site. Stimulated a Dwivedi and Chaudhary, 2012 well organized fibrous tissue proliferation, epithelization and complete scar [277] formation Ethanolic extract of Annona squamosa STZ diabetic rats Enhanced rates of epithelialisation and wound contraction. Increased cellular Ponrasu et al, 2012 [278] proliferation and collagen synthesis at the wound site L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114 7097

grade 0 (no ulcer in a foot with a high-risk factor of complica- tion); grade 1 (partial/full thickness ulcer); grade 2 (deep ulcer, penetrating down to ligaments and muscle, but no bone involve- [283] ment); grade 3 (deep ulcer with cellulitis or abscess formation); [281]

[279] grade 4 (localized gangrene); and grade 5 (extensive whole foot [280]

[282] gangrene) [64]. The classification of DFUs is important as it may facilitate the choice of suitable dressing depending on the wound type and on its phase [65]. This choice depends on several factors that will be discussed in Bitto et al, 2008 Bagheri et al, 2011 McLaughlin et al, 2011 the following sections.

3. Wound dressings for DFU treatment

3.1. Types and main characteristics of wound dressings

Natural skin is considered the perfect wound dressing and therefore an ideal wound dressing should try to replicate its prop- erties [66]. Historically, wound dressings were first considered to play only a passive and protective role in the healing process. However, in recent decades wound treatment has been revolu- tionized by the discovery that moist dressings can help wounds heal faster [67,68]. Furthermore, a moist wound environment is also an important factor to induce the proliferation and migration of fibroblasts and keratinocytes as well as to enhance collagen synthesis, leading to reduced scar formation [69,70]. Besides assuring optimal moisture for wound environments, it is currently accepted that a wound dressing should also: (i) have the capacity to provide thermal insulation, gaseous exchange, and to help drainage and debris removal thus promoting tissue recon- struction processes; (ii) should be biocompatible and not provoke any allergic or immune response reaction; (iii) should protect the wound from secondary infections; and (iv) should be easily re- moved without causing trauma [66,71]. Due to the distinct characteristics of the different types of wounds and of each of the wound healing stages, there is no collagen fibers, numerical density ofincreased fibroblasts and length density of vessels were wound content at day 6 impairing the wound healing process facilitating wound healing process one single dressing that can be efficiently applied in all situations [72]. However, it is possible to develop and to optimize different biocompatible wound dressing materials in terms of their chem- ical and physical properties, e.g. moisture absorption and perme- ation capacities, in order to meet most of the needs for a particular wound stage [73]. In general terms and according to their main types and char- acteristics, the most commonly used wound dressings for dia- betic wound healing applications can be easily classified as follows:

(1) Hydrocolloids—these systems are moist wound dressings and usually comprise a backing material (e.g. semi-perme- able films, foams or non-woven polyester fibers) and a layer with hydrophilic/colloidal particles that may contain biocompatible gels made of proteins (e.g. collagen, gelatin) or of polysaccharides (e.g. cellulose and its derivatives) [67,74,75]. When in contact with wound exudate, these dressings will absorb wound fluids, thus creating a moist environment [75,76]. They also have the capacity to be semi-permeable to water and oxygen [74]. However, the application of hydrocolloid dressings in strongly infected wounds has been questioned due to the possible hypoxic Azelnidipine STZ diabetic rats Accelerated wound healing and improved NO levels in wound fluid. Also, density of Simvastatin db/db diabetic mice Increased VEGF mRNA and protein expression. In addition, simvastatin enhanced NO Ciclopirox olamineNaltrexone db/db diabetic mice STZ diabetic rats Enhanced wound closure, increased angiogenesis and dermal cellularity Reduced wound area in 50% compared with control; Ko stimulated et DNA al, synthesis 2011 and excessively moist environment that could potentiate autolysis of necrotic tissue and therefore increase the risk of infection at the wound site [77,78]. Hydrocolloids are usually applied to granulating and epithelializing wounds and therefore they may be also used for necrotic wounds in order to promote wound debridement [76]. In average,

Other Nicotine db/db diabetic mice Accelerated healing and increased wound angiogenesisthese materials Jacobi et al, 2002 can be maintained on DFUs for more than 7098 L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114

one week [74]. However, there are contradictory studies on wounds and in applications that usually last 4–5 days before whether hydrocolloid-type wound dressings can be used in the dressing is replaced [73,74,77]. However, they may be diabetic foot wounds in the case of superficial wounds, if used directly on the wound or in association with other there are no signs of infection, or if few or moderate wound types of dressings in order to better fix those in the wound exudates are present [78]. bed or to improve their fluid barrier properties [69,73]. (2) Hydrogels—these systems are mostly used to maintain highly Film-type dressings have been also developed and employed moist wound environments and are comprised of single or in DFU treatment [74]. The main characteristics of each of mixed hydrated polymers (i.e. in the form of a gel) present- these materials are summarized in Fig. 3. ing at least 20% of their weight in retained water [73,79].If the water content is higher than 95%, these materials are Different synthetic and natural polymer-based biocompatible usually designated as superabsorbents [77]. Hydrogels may materials, as well as their mixtures or combinations and different be covalently or non-covalently cross-linked in order to con- processing methodologies, have been proposed and assayed both trol their swelling capacities and to maintain their confor- in vitro and in vivo for wound dressing (and DFU) applications mational structures [67], and they may swell (or shrink) [84–86]. Some of these materials are already commercially avail- reversibly in aqueous environments of specific pH and ionic able and in clinical use [87,88]. To supplement and enhance the strength values [80]. Like hydrocolloid dressings, hydrogels general wound dressing functions several different strategies have are capable of promoting the autolytic debridement of been developed, namely those involving the incorporation of bio- necrotic tissues and are usually more efficient at drying active compounds (e.g. growth factors, peptides, synthetic drugs wounds with few exudates [79]. Their application in wounds and/or naturally based compounds/extracts) and of stem cells into having excess exudate can cause wound maceration and dressing matrices in order to prepare medicated dressings lead to healing problems [81]. A great advantage of hydro- [89–92]. gel-type wound dressings is that they can usually be applied/removed without greatly interfering with the 3.2. Polymeric wound dressings for DFU treatment wound beds [73,74]. In addition, these dressings are flexible, non-antigenic, and permeable to water, oxygen and metab- Wound healing efficiency depends on several factors such as the olites [67]. wound type and stage, the extent of injury, patient condition, the (3) Foams—foam-type dressings were developed as alternatives tissues involved, as well as on the dressing selected, and on the ef- to hydrocolloid-type dressings for applications in moderate/ fect of healing enhancers and therapeutic substances (if em- high draining wounds [82]. Their capacity to absorb wound ployed). Wounds can be treated using passive or hydroactive fluids is in general dependent on the specific polymeric dressings [93]. The first are usually used for acute wounds (as they material employed and on the foam thickness [73]. These absorb reasonable amounts of exudates and they can ensure good dressings are highly absorbent, cushioning, protective and protection), while the latter are normally used for chronic wounds conformable to body surfaces [83]. Moreover, they are easy (as they easily adapt to wounds and are able to maintain a moist to manipulate and can be adapted to the required wound environment that can stimulate the healing process) [83]. In both size [74,77]. Due to their absorbency and protective charac- cases, and as already noted, drugs and/or other healing enhancers teristics, foam-type dressings can be left on the wound for can be incorporated into the wound dressing polymeric matrices up to seven days [83]. Therefore, foams have been also pro- mostly to improve and accelerate healing. posed as potential candidates for DFU treatment [77,82]. Different constituent polymeric materials, exhibiting distinct (4) Films—these types of wound dressings are normally trans- chemical, physical and biological properties, may be employed in parent, durable, conformable, easy to manipulate, adhesive, the preparation of wound dressing systems of different designs, cheap, semi-permeable to oxygen and water vapor, and dimensions and shapes, in order to obtain final products offering often impermeable to liquid and to bacterial contamination different final functional properties [72,94]. One of the simplest [73,83]. The main disadvantage of film-type dressings is that ways to differentiate those polymeric materials is by considering they should only be used for wounds with few exudates, their origin: synthetic or naturally based polymers and copolymers namely as protective dressings in superficial pressure [95]. Modified polymeric materials (those obtained by chemical

Fig. 3. Classification of the different dressing types usually used in DFU treatment. Table 2 Recently natural and synthetic based dressings studied for DFU application.

Polymers Bioactive substance Models used Results References Chitosan and Chitosan-crosslinked collagen Recombinant human STZ diabetic rats Accelerated wound healing promoting a faster tissue collagen deposition, Wang et al, 2008 derivatives aFGF higher TGF-b1 expression and dermal cell proliferation. [284] Chitosan with different degrees of Acetylglucosamine Human diabetic Decreased wound size and stimulated angiogenesis and reepithelialization Ben-shalom et al, deacetylation oligomers after seven days. 2009 [285] Thiolated chitosan-oxidized dextran À STZ diabetic mice Showed to be non-cytotoxic, resistant to degradation and capable of Zhang et al, 2011 hydrogel stimulate tissue regeneration. [286] Chitosan, alginate, and poly( c-glutamic À STZ diabetic rats Enhanced wound healing. Stimulated collagen deposition, hydroxyproline Lee et al, 2012 [85] acid) hydrogel levels and promoted skin epithelialization. Showed antibacterial properties. Hyaluronic acid HA benzyl ester films Autologous human Human patients with non Induced healing of 79% of DFUs between 7 and 64 days. Lobmann et al, and derivatives keratinocytes healing DFU 2003 [287] Poly-N-acetyl glucosamine (pGlcNAc) À db/db diabetic mice Wounds dressed reached 90% closure in 16.6 days, 9 days faster than Scherer et al, 2009 untreated wounds. Higher levels of proliferation and vascularization were [288] observed in granulation tissue.

High molecular weight sodium hyaluronate Iodine complex- Human patients with DFUs Reduced significantly the size of diabetic ulcers. Sobotka et al, 2007 7093–7114 (2013) 9 Biomaterialia Acta / al. et Moura L.I.F. Hyiodine [289] pGlcNAc membrane À db/db diabetic mice Accelerated wound closure mainly by reepithelialization and increased Pietramaggiori keratinocyte migration, granulation tissue formation, cell proliferation, and et al, 2008 [290] vascularization. Up-regulated levels of VEGF, uPAR and MMP3, MMP9. High molecular weight HA gel À STZ diabetic rats Reduced wound size and increased the number of macrophages, fibroblast Bayaty et al, 2010 migration, collagen regeneration and epithelization of the wounds. [291] Cross-linked high and low molecular weight Arginine and EGF STZ diabetic rats Significantly decreased wound size and increased the epithelization. In Matsumoto and HA foam addition, enhanced the early-stage inflammation. Kuroyanagi, 2010 [89] HA gel (Vulcamin) Mixture of amino Human patients with After 3 month, the ulcer area and the number of infective complications Abbruzzese et al, acids neuropathic ulcers were clearly decreased. 2009 [292] Cellulose and Cellulose dressing Silver nanoparticles Human patients with DFUs Decreased the activity of Escherichia coli and of Staphylococcus aureus Jung et al, 2009 derivatives bacteria by 99.99% in wounds. [149] Collagen/oxidized regenerated cellulose À Human patients with Application in neuropathic DFUs during 6 weeks stimulated wound healing. Lazaro-Martinez foam neuropathic DFUs et al, 2010 [293] Microbial-derived celullose hydrogel Polyhexamethylase Human patients with non- Inhibit the proliferation of bacteria, provided an optimal moist healing Serafica et al, 2010 biguanide (PHMB) healing ulcers environment through the absorption of excess fluid from exudating [150] wounds. Remove necrosis and hyper granulation tissue to normal levels. Improvement in healing process was verified. Collagen/oxidized regenerated cellulose À Human patients with non- Significant decrease the expression of proteases, such as elastase, plasmin, Ulrich et al, 2011 foam healing DFUs and gelatinase in wound exudates. [294] Microbial cellulose À Human patients with non- Treated wounds healed after 32 days which was faster than the 48 days Solway et al, 2011 infected DFUs necessary to heal control wounds. [142] Choi et al, 2012 Carboxymethyl celulose hydrogel Chestnut honey db/db mice Significantan early-induction reduction of of HO-1 wound were area, verified an increase at the of wound tissue site. granulation and [295] Alginate Alginate hydrogel Phenytoin Human patients with DFUs Eradicated infection, reduced pain and led to 60% of wound closure after 16 Shaw et al, 2011 weeks of treatment. [296] Alginate gel Honey Human patients with DFUs Satisfactory healing and stimulated tissue reepithelization. Molan et al, 2011 [297]

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Table 2 (continued)

Polymers Bioactive substance Models used Results References Collagen/Gelatin Gelatin microspheres bFGF db/db mice Reduced infection, accelerated fibroblast proliferation and capillary Kawai et al, 2005 formation. [185] Colagen dressing À Human patients with DFUs 60% of them healed after two weeks of treatment. A decrease of infection by Singh et al, 2011 bacteria and an augment of granulation tissue were also observed. [181] Ò Collagen matrix, Integra (Integra À Human patients with DFUs Salvaged 46% of the limbs, increased the bacterial clearance and created a Iorio et al, 2011 LifeSciences Corp., USA) at high risk of amputation bed of granulation tissue. [298] Collagen matrix Glucose oxidase STZ diabetic rats Increased cellular proliferation and stimulated a faster wound contraction. Arul et al, 2012 [182] Collagen–gelatin foam bFGF db/db mice Accelerated dermis tissue formation and increased the number of new Kanda et al, 2012

capillaries. [186] 7093–7114 (2013) 9 Biomaterialia Acta / al. et Moura L.I.F. Fibrin Fibrin scaffold AdeNOS alloxan diabetic rabbit Enhanced wound healing, eNOS expression, the inflammatory response and Breen et al, 2008 led to a faster rate of re-epithelialisation in an. [98] Combined single-donor platelet gel and À Human patients with DFUs Stimulated wound closure. Chen et al, 2010 fibrin glue [188] Ò Leucopatch (naturally coagulated fibrin) À Human patients with DFUs Wound area decreased significantly by 65%. Jorgensen et al, 2011 [299] Fibrin gel CD34 +cells STZ-diabetic mice Stem cells together with fibrin gel enhanced wound healing. Pedroso et al, 2011 [189] Silk fibroin Fibroin film Aloe vera extract STZ diabetic rat Enhanced wound healing. Inpanya et al, 2012 [193]

Dextran Dextran-allyl isocyanate-ethylamine/ À Human patients with Promoted dermal regeneration, facilitated the early inflammatory cell Sun et al, 2011 polyethylene glycol diacrylate hydrogel chronic wounds infiltration and promoted cell migration into the wounds. [197] Elastin Elastin-like peptides gel KGF STZ diabetic mice Enhanced reepithelialization and granulation tissue. Koria et al, 2011 [199] PVA PVA aminated hydrogel NO db/db mice Increased collagen production, enhanced the quality of the granulation Bohl et al, 2002 tissue and increased the wound strength. [215] Aminophenyl boronic acid with PVA Ciprofloxacin Diabetic human patients Promoted an efficient release of anti-bacterial drugs to improve Manju et al, 2010 complications in long term healing wounds. [216] PEG PCL-PEG block copolymer rhEGF STZ diabetic mice Induced faster wound healing with high proliferation and keratinocytic Choi et al, 2008 expression at the wound site. [229] PEG-PCL nanofibers EGF and bFGF STZ diabetic mice Increased the accumulation of collagen and keratin and reduced scar Choi et al, 2011 formation. [230] PEGylated fibers rhaFGF STZ diabetic rats Stimulated wound closure, tissue collagen formation and earlier and higher Huang et al, 2011 TGF-b expression. [227] Poly(ethylene imine) and PEG plasmid bFGF STZ diabetic rats Significantly increased the wound recovery rate, enhanced collagen Yang et al, 2012 deposition and maturation and complete re-epithelialization. [226] PVP Poly (vinyl methyl ether co-maleic NO STZ diabetic rats The complex controlled release of NO and accelerated wound closure. Li and Lee, 2010 anhydride) and PVP [234] L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114 7101

modification of naturally based polymers) [96] or mixtures/com- binations of different polymers and copolymers [97] can also be considered. For DFU applications, a wide variety of polymeric materials has

[247] already proved to enhance healing and some of these are now commercially available [98,99]. Varma et al, 2008 [238] Rayment et al, 2010 Dong et al, 2008 [252] [255] [253] Yang et al, 2011 [99] Some of the commonly used polymer-based materials used to produce dressings for DFU treatment will be presented hereafter and a brief description of their structure–property relationships are provided in Table 2. Some examples of commercial dressings currently available for this purpose are also described in Table 3.

3.2.1. DFU dressings based on natural polymers Natural polymers can be classified as those obtained from microbial, animal or vegetal sources that are usually of a protein or polysaccharide nature [100]. Although these naturally occur- ring polymers can closely simulate the original cellular environ- ments and ECMs, and these biomaterials are known to undergo naturally controlled degradation processes, their large heteroge- neity and batch-to-batch variations upon their isolation from animal or vegetal tissues are the main limitations for their appli- cations [101,102]. Other concerns include the relatively high cost of some of these materials (namely of protein-based materials) and the associated risk of the transmission of infectious diseases due to the allogenic or xenogenic origins of the original materials [101]. Poor stability and mechanical performance also represent drawbacks that may limit their wider application [103]. However, various chemical synthesis and/or processing modifications may Maintain a moist wound environmentexudates and and to dead absorb tissues. the excessive wound necessary MMP levels for normal healing are not affected in the wound bed. regeneration of skin appendages, highervessels. density and mature capillary efficiently. be performed in order to overcome some of these disadvantages [84]. Blending these materials with other polymeric materials (including synthetic polymers) is another viable alternative for in this respect [104]. The natural polymers that are being em- ployed in the preparation of wound dressings, and particularly for DFU treatment, will be presented and discussed in the follow- ing sections.

3.2.1.1. Chitin, chitosan and derivatives. Chitin is one of the most abundant polysaccharides in nature. It can be found in the exo- Human patients with lower limb wounds skeleton of arthropods, of crustacea, of some mollusks and in the cell walls of fungi [105]. Common chitin sources (e.g. shells of shrimps and crabs) are very accessible at low cost, making chi- tin a commercially attractive biomaterial for various applications [106,107]. Chitin is a linear polysaccharide of N-acetyl-D-glucosa- mine (2-acetylamino-2-deoxy-D-glucose) units linked by b-(1-4) glycosidic bonds [84,108–111]. As chitin is not soluble in aqueous À solutions, it is usually converted into chitosan by thermochemical deacetylation in the presence of an alkaline solution [111,112]. Therefore, chitosan is a linear copolymer of D-glucosamine and of N-acetyl-D-glucosamine. The term chitosan is also usually em- ployed to describe a series of chitin derivatives having different degrees of deacetylation (defined in terms of the composition of primary amino groups in the polymer backbone and of their aver- age molecular weights) [112]. The chemical, physical and biological properties of chitosan are directly related to its deacetylation degree and to its molecu- lar weight [113], and chitosan is generally regarded to be biode- gradable, biocompatible, non-antigenic, non-toxic, bioadhesive, anti-microbial, bioactive and to have hemostatic effects

PCL nanofibersPLGA nanoparticlesPLA fibers Curcumin rhEGF STZ diabetic mice bFGF STZ diabetic rats These nanofibres increased the rate of[103,105,114] wound closure. Promoted a STZ faster diabetic healing rats rate as well as fibroblast proliferation.. It Higher wound recovery Chu is rate et with al, complete 2010 Merrel re-epithelialization, et also al, 2009 easily degraded by chemical hydrolysis as well as by certain human enzymes, namely lysozyme [109,110]. In addition, chitosan amino and hydroxyl groups can be easily reacted and chemically modified, thus allowing a high

-esters) PLGA microspheres rhEGF STZ diabetic rats Enhanced the growth rate of fibroblasts andchemical the wound healed more versatility. For example, chitosan may be modified into a N-carboxymethyl chitosan [115], N-carboxybutyl chitosan [116,117], N-succinyl chitosan [118], N-acyl chitosan [119], N,O- PU PU-based foam PHEMAPoly ( PHEMA and by PEG hydrogel MMP inhibitors Human patients with DFUs MMPs in the chronic wound fluid are inhibited while guarantying that the (carboxymethyl) chitosan [120], N-N-dicarboxymethyl chitosan 7102 L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114

Table 3 Commercial dressings used for DFU treatment.

Commercial dressing Fabricant Composition Main characteristics

BionectÒ Dara BioScience 0.2% of sodium salt of hyaluronic acid  Easy to use  Reduces the incidence of high-grade skin reactions  Reduces wound severity UniteÒ Biomatrix Synovis Non-reconstituted collagen  Collagen dressing helps maintain wound bed in healing phase Orthopedic and  Allows for healthy granulation tissue and wound closure WoundCare, Inc.  Absorbs excess exudate allowing few dressing changes  Easily conforms to the wound bed  Strong and durable BGC MatrixÒ Mölnlycke Collagen and the advanced carbohydrate  Protects underlying tissue from external contamination Health Care US, beta-glucan  Provides structural support for new cell growth LLC  Adherent, flexible and conformable  Minimizes protein and water loss  Collagen aids in hemostasis  Minimizes pain Promogran PrismaÒ Matrix Systagenix Collagen, ORC and silver-ORC matrix  In the presence of exudate, the matrix transforms into a biode- gradable gel  Provides protection from infection and optimal healing environment  Designed to ‘‘kick start’’ the healing process in stalled wounds  Biodegradable gel is soft and conformable  Can be used under compression therapy  Non-toxic and non-irritating  Easy to use Dermacol/Ag™ DermaRite Collagen, sodium alginate, carboxyl  Transforms into a soft gel sheet when in contact with wound Collagen Matrix Industries methyl- cellulose, ethylenediamine- exudates Dressing with Silver tetraacetic acid (EDTA) and silver chloride  Maintains a moist wound environment, and creates ideal con- ditions for healing  Antimicrobial silver chloride prevents colonization of the dressing  Easy to use FibracolÒ Plus Collagen Wound Systagenix Collagen and calcium alginate fibers  Structural support of collagen with gel forming properties of Dressing with Alginate wound alginates  Maintains a moist wound environment, and creates ideal con- ditions for healing  Adherent, flexible and conformable  Sterile and soft Aquacel HydrofiberÒ Wound ConvaTec Antimicrobial hydrofiber containing  Absorbs wound fluid and creates a soft gel, which maintains a Dressing carboxymethyl cellulose with ionic silver moist wound environment  Absorbs and retains exudate and harmful components, such as bacteria contained within exudate, directly into its fibers  Helps reduce the pain and trauma upon dressing removal  Conforms to the wound surface  Used on moderately and highly exuding chronic wounds RegranexÒ Gel Healthpoint rh PDGF-BB incorporated in aqueous  Stimulates wound healing processes and aids in creation of Biotherapeutics sodium carboxymethylcellulose granulation tissue  Only FDA-approved topical agent with platelet-derived growth factor  Promotes the recruitment and proliferation of chemotactic cells  Stimulates wound closure  Easy to use MediHoneyÒ Derma Sciences, 80% active Leptospermum honey with  Maintains effectiveness even in the presence of wound fluid, Adhesive Inc. colloidal alginate blood and tissue Honeycolloid  For wounds with light to moderate amounts of exudates Dressing  Pad will form a gel as it warms up and contacts wound fluid  Promotes a moisture-balanced environment conducive to wound healing  Helps wounds that have stalled progress toward healing  High osmolarity cleanses  Helps lower overall wound pH  Non-toxic, natural, safe and low-cost MediHoneyÒ Derma Sciences, Contains 95% active Leptospermum honey  As wound fluid enters the dressing, the honey is released Calcium Alginate Inc. with calcium alginate while the dressing forms a gel Dressing  Maintains effectiveness even in the presence of wound fluid, blood and tissue  Promotes a moisture-balanced environment conducive to wound healing  Highly osmotic and helps to reduce overall wound pH  For wounds with moderate to heavy amounts of exudates  Non-toxic, natural, safe and easy to use L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114 7103

Table 3 (continued)

Commercial dressing Fabricant Composition Main characteristics

Algisite⁄ Smith & Nephew, Calcium-alginate  Forms a gel that absorbs exudate when in contact with wound Calcium Alginate Dressing Inc.  Helps prevent scar formation and promotes wound contraction  Allows gas exchange necessary for a healthy wound bed  Low-adherence reduces trauma at dressing changes  Conforms to wound contours  Low fiber shed  Easy to remove SorbalgonÒ Hartman USA, Calcium alginate  Forms a hydrophilic gel on contact with wound exudate Inc.  Maintains integrity while dry or wet  High absorbent  Easy to remove  Latex-free KaltostatÒ Dressing ConvaTec Sodium and calcium salts of alginic acid  In the presence of exudate or other body fluids containing sodium ions, the fibers absorb liquid and swell  Calcium ions present promote the dressing to take on a gel- like appearance  Facilitates wound healing providing a favourable micro- environment  Easy to use Tegaderm™ High Gelling 3 M Health Care Polyurethane dressing containing alginate  Forms a gel-like consistency as it absorbs exudate to provide a Alginate Dressing moist healing environment  Completely gels with saturation for easy removal from fragile tissue by gentle irrigation  Easily irrigated from the wound bed when saturated  Highly absorbent dressings and conformable GranuDerm™ Acute Care Alginate hydrocolloid with polyurethane  Breathable film membrane surrounds the wound site Sentry™ Solutions, LLC  Promotes wound repair  Visually signals dressing changes  Water, dirt and germ proof  Reduces dressing changes  Extended wear time  Prohibits leakage BiatainÒ Heel Foam Dressing Coloplast Corp. 3-D non-adhesive foam of polyurethane  Foam absorbs and retains wound exudate to control moisture balance in wound  Absorbs low-to-high wound exudate levels and protects the heel  Decrease wound are and prevents skin maceration  Soft, beveled edges makes dressing more comfortable for patient  Longer wear time for fewer dressing changes  Low risk of leakage or maceration  Safe and effective Biatain Ibu Foam Dressing Non- Coloplast Corp. Combination of polyurethane-foam,  Combines moist wound healing with an active pain reliever adhesive polyurethane film, polyethylene and  Releases ibuprofen evenly into the wound ibuprofen  Helps to ease pain from the wound during wear and when changing the dressing  Promotes wound repair  Easy to use MANUKAhdÒ ManukaMed Polyurethane foam and film in backing  100% active medical grade ManukaÒ honey USA, Inc. and an absorbent dressing pad of  Gentle on wounds promoting wound healing polyacrylate polymers impregnated with  Forms gels in contact with exudate ManukaMedÒ honey  Fluid permeable and dry-touch DuoDERMÒ CGFÒ ConvaTec Polyurethane foam  Promotes granulation and facilitates autolytic debridement  Can be easily and gently molded into place  Use on lightly to moderately exuding acute and chronic wounds  Minimize skin trauma and disruption of healing  Can be worn for up to 7 days  Allows observation of the healing process due to its transparency SOLOSITEÒ Conformable Wound Smith & Nephew, Polyurethane and polyethylene hydrogel  Creates a moist wound healing environment Gel Dressing Inc.  Keeps gel in intimate contact with wound surface  Absorbs excess exudate allowing few dressing changes  Non-cytotoxic and non-sensitizing SilverlonÒ Island Wound Argentum Polyurethane film containing silver  Non-adherent wound contact layer Dressing Medical, LLC  Provides effective protection against microbial contamination  Permits passage of wound exudate  Stimulates wound repair  Easy to apply

(continued on next page) 7104 L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114

Table 3 (continued)

Commercial dressing Fabricant Composition Main characteristics

Allevyn Smith & Nephew, polyurethane films combined with  Minimizes pain to the patient and trauma to the wound at Inc. polyurethane foam containing 5% silver dressing change sulphadiazine.  Rapid and sustained (7 days) antibacterial action  Absorbs, retains and transpires exudate to provide enhanced fluid management  Provides a moist wound environment for the promotion of faster closure  Stays in place for up to 7 days Meliplex Ag Molnlycke Heath Polyurethane foam containing a silver  Vapor-permeable Care compound (silver sulphate)  Waterproof film to absorb exudate  Maintains a moist wound environment Ligasano Ligasano Honeycomb-polyurethane foam  Economic and manageable  Absorbs high amounts of exudate without dehydrating the wound bed  Creates a moist and warm wound environment  Antiseptic and cleans the wound with no sticking to the wound  Stimulates local blood circulation in the wound

[121], N-carboxyethyl chitosan [122], O-succinyl chitosan [123], O- sustained delivery of growth factors, etc. The main achievements carboxymethyl chitosan [124], 5-methylpyrrolidinone [125] and recently obtained with chitosan-based dressings for wound heal- more. The conditions employed for amino group chemical modifi- ing (with the focus on DFU) treatments are summarized in Table 2. cation may interfere with the final degree of deacetylation and therefore with the cationic nature of the obtained materials. Chito- 3.2.1.2. Hyaluronic acid and other glycosaminoglycans. Hyaluronic san exhibits a pH-sensitive behavior being a weak poly-base (due acid (HA) is a natural polysaccharide, namely a non-sulfated gly- to the large number of amino groups). Chitosan easily dissolves cosaminoglycan (GAG), which is a major component of the ECM at relatively low pH values (while it is insoluble at higher pH val- of the connective tissues of certain mammals such as cartilage, ues, usually above pH 6.0) and its pH-sensitive swelling mecha- eye vitreous humor, umbilical cord and synovial fluid [67,101]. nism involves the protonation of the amine groups under these HA is also referred to as hyaluronan due to the fact that it usually low pH conditions [105,126]. Chitosan is also soluble in weak or- exists in vivo as a polyanion and not in the protonated acidic form ganic acids, interacting with negatively charged molecules, which [133]. It is a linear polysaccharide of alternating disaccharide units may facilitate its processing and further integration into particles, of a-1,4-D-glucuronic acid and b-1,3-N-acetyl-D-glucosamine, membranes, fibers or sponges [107,127]. This property has led linked by b(1?3) glycosidic bonds [126]. HA is usually extracted chitosan and its derivatives (alone or combined/conjugated with from the umbilical cord, vitreous humor, synovial fluid or from other polymeric materials) to be widely studied as delivery matri- rooster combs [134]. When extracted from the host body, HA is ces for a number of pharmaceutical applications [96,105,128,129]. non-allergenic and biocompatible [135,136]. However, it is already At acidic pH, chitosan is positively charged and therefore it is more easily produced on a large scale and in a controllable and reproduc- susceptible to interaction with negatively charged molecules such ible way by microbial fermentation [133]. HA is water soluble up to as proteins, anionic polysaccharides and nucleic acids, which are certain concentrations and can produce highly viscous solutions usually present in skin [67,130]. with unique viscoelastic properties. It can form three-dimensional In addition to the fact that chitosan-based materials usually ex- structures in ex vivo aqueous solutions through hydrogen bonding hibit a positive charge (at typical wound pH values), film-forming [133]. capacities, mild gelation characteristics and strong wound tissue HA presents many important physiological functions such as adhesive properties, chitosan and its derivatives were also found structural and space-filling properties, lubrication, as well as tissue to enhance blood coagulation and to accelerate wound healing and ECM water sorption and retention abilities [135,137].HAis [84,109]. Therefore, these materials clearly present several proper- also an interesting biomaterial for wound healing applications ties that can potentially permit their use as advantageous and effi- since it is known to promote mesenchymal and epithelial cell cient wound dressings. In particular, chitosan films of low migration and differentiation, thus enhancing collagen deposition deacetylation degree have already proved to be efficient for dress- and angiogenesis [133,136,138]. ing superficial wounds [111]. Other works also indicated that these HA’s chemical and physical properties, namely its mechanical biomaterials enhance the inflammatory functions of polymorpho- properties and degradation profiles, are strongly dependent on its nuclear leukocytes, macrophages and neutrophils, promoting tis- molecular weight. Native high molecular weight HA has important sue granulation to an appropriate inflammatory response [131]. structural properties, whereas its degradation products may stim- Moreover, chitosan may stimulate the proliferation of fibroblasts, ulate endothelial cell proliferation and migration, modulate the angiogenesis, synthesis and a regular deposition of collagen fibers inflammatory processes and promote angiogenesis during the dif- that leads to improved tissue organization [84,109,132]. ferent wound healing stages [137,139,140]. A large number of Chitosan can be also complexed/cross-linked with other studies involving the use of HA in the context of DFU, processed charged or non-charged polymers and/or cross-linking agents to as foams or gels, with or without bioactive substances, have been change/enhance its physical/chemical/mechanical properties. reported and these are summarized in Table 2. Through this approach it is possible to optimize and/or to design chitosan-based dressings with improved healing characteristics 3.2.1.3. Cellulose and its derivatives. Cellulose is the primary struc- that include enhanced adherent and anti-bacterial capacity, in- tural component of plant cell walls and is the most abundant or- creased exudate absorption capacity, stimulation of angiogenesis ganic polymer on Earth. Therefore, it is a renewable biomaterial, and re-epithelialization of skin tissue and collagen deposition, readily available at low cost [101]. Furthermore, it can also be eas- L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114 7105 ily converted into several potentially advantageous derivatives. Alginates can form reversible hydrogels through the interaction 2+ 2+ 2+ 2+ Cellulose is a linear polymer constituted by b-1,4 linked D-glucose with divalent cations, such as Ca ,Mg ,Ba or Mn , that can units which are joined to form cellobiose repeating units [141]. cross-link G-residues of adjacent alginate chains by means of ionic Cellulose glucan chains are parallel and are packed side-by-side, interactions [152]. Despite other applications, these easy cross- forming microfibrils, stabilizing the structure but minimizing its linking and processing strategies allow their wide use as three- flexibility. The degrees of polymerization and the molecular orga- dimensional supports for cell transplantation, as well as wound nization of its chains are the main characteristics that affect the dressing biomaterials. Moreover, alginate has high biocompatibil- chemical and physical properties of cellulose and thus its process- ity, low toxicity and good mucoadhesive properties ing methods and applicability [142]. This highly cohesive hydro- [101,141,153]. Alginate-based biomaterials are also pH sensitive gen-bonded structure provides cellulose fibers of great stability, and the release of bioactive species from these materials at low rigidity and tensile strength and makes them water insoluble (de- pH conditions is significantly reduced. Therefore, this feature could spite their hydrophilic character). Cellulose and its derivatives are be advantageous for the development of a delivery system in- slightly degradable by several bacteria and fungi present in air, tended for near-neutral pH conditions [152]. water and soil, which leads to a decrease in its mechanical strength However, alginate-based hydrogels may present unpredictable and to an improvement in its water solubility [141,143]. In addi- and uncontrollable degradation and dissolution profiles after loss tion, cellulose-based materials are considered biocompatible due of the divalent cation cross-linkers [153]. To overcome this issue, to their reduced inflammatory response to foreign bodies covalent/ionic cross-linking can be employed with other biopoly- [143,144]. Moreover, resorption of cellulose in tissues does not oc- mers such as gelatin [154], heparin [155], polyvinyl alcohol [156] cur since cells are not able to synthesize cellulases [144]. and chitosan [157]. The other main disadvantage of alginate-based Some cellulose ether derivatives such as methyl cellulose, materials is their inability to undergo efficient and rapid enzymatic hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxyethyl degradation in mammals. In addition, alginates are very hydro- methyl cellulose, hydroxypropyl methyl cellulose and carboxy- philic, which hinders its interactions with skin proteins [152]. methyl cellulose are cold and/or hot water-soluble up to some con- Calcium alginate-based dressings are recognized to have the centrations and present other interesting properties such as capacity to efficiently absorb wound exudates, hence facilitating organic-solvent solubility, thermoplastic behavior and biosurface debridement and accelerating wound healing in DFU activity. Cellulose ester derivatives, such as cellulose acetate, cellu- [82,158,159]. Alginate-based dressings have also been combined lose triacetate and cellulose sulfate, are also fiber- and film-form- with growth factors such as stromal derived factor-1 (SDF-1) or ing materials [145]. Moreover, their molecular weights can be drugs such as phenytoin, ibuprofen or clindamycin to improve varied, and therefore their aqueous viscosities and gelation proper- DFU treatment. Commercial products such as Medihoney (Derma ties can be tuned [143,146]. These features allow their use in sev- Sciences Inc., Canada) which is an alginate hydrocolloid wound eral pharmaceutical formulations and for various biomedical dressing loaded with a minimum of 70% of active Leptospermum purposes. honey or Algisite M Calcium Alginate Dressing (Smith and Nephew Microbial (or bacterial) cellulose (MC) is different from plant- Inc., Australia) are alginate-based dressings indicated for DFU origin cellulose. It is synthesized by various bacteria and has al- treatment. These and other examples of the application of alginate ready proved to present great potential for wound healing applica- dressings for DFU wound healing are summarized in Table 2. tions [147,148]. Its high mechanical strength, crystallinity and high capacity to retain water mostly arise from its unique nanofibrillar 3.2.1.5. Collagen and gelatin. Collagen is the most abundant protein structure [143,147]. of the ECMs naturally present in human tissues (e.g. skin, bone, Some studies have demonstrated that cellulose stimulates cartilage, tendon and ligaments). It represents 25% of the total pro- wound healing through the release and maintenance of therapeu- tein body content [80,102,160,161], providing strength and integ- tic levels of a number of growth factors (i.e. PDGF, epidermal rity to tissue matrices [162]. In addition, collagen can also growth factor (EGF) and FGF) at the wound site and by promoting interact with cells and help essential cell signaling that will regu- dermal fibroblast migration and proliferation and inhibiting bacte- late cell anchorage, migration, proliferation, differentiation and rial proliferation in wounds [149–151]. In this last case a signifi- survival [101,120,162]. cant improvement was observed by loading the dressing material Twenty-seven types of collagens have already been identified, with antimicrobial agents such as polyhexamethylase biguanide with types I–IV being the most common. Type I collagen is the (PHMB) or silver. The biocompatibility of cellulose-based materials most abundant protein present in mammals and is the most stud- has been achieved by combining cellulose with other polymers ied protein for biomedical applications [101,141]. such as collagen. An example of a commercial cellulose-based Collagen degrades enzymatically within the body, mostly via dressing is AquacelÒ Hydrofiber WoundDressing (ConvaTec, USA), collagenases, gelatinases and metalloproteinases [163]. In general which is an antimicrobial carboxymethyl derivative of cellulose terms, collagens are rod-type proteins with typical molecular that can absorb wound fluids and create a gel to maintain a moist weights around 300000 g molÀ1 that also present high mechanical wound environment for proper wound healing. These and other strength and good biocompatibility (although they may present achievements obtained after the use of cellulose-based dressings some antigenicity) [101,164]. Collagen can form stable fibers and in the context of DFU healing are summarized in Table 2. its mechanical, degradation and water-uptake properties can be further enhanced by chemical cross-linking (using glutaraldehyde [165], genipin [166], carboiimide [167], hexamethylene diisocya- 3.2.1.4. Alginate. Alginate (or alginic acid) is one of the most stud- nate [168]), by physical cross-linking (using freeze-drying) [169] ied and applied polysaccharides in tissue engineering and drug or by binding with other protein/polymers [170,171]. Low inflam- delivery applications. It is abundant in nature since it is a structural matory and cytotoxic responses and biodegradability are other component of marine brown algae (Laminaria hyperborean, attractive properties of collagen [102]. Ascophyllum nodosum and Macrocystis pyrifera) and as capsular As a result, and since collagen is one of the major components of polysaccharides in some soil bacteria [101]. It is constituted by human ECMs, it is usually considered as an ideal biomaterial for b-D-mannuronate (M-residues) and a-L-guluronate (G-residues) tissue engineering and for wound dressing applications. Collagen residues covalently linked in different alternating or random is usually isolated from animal tissues, a source that raises some sequences/blocks [101,141,152]. concerns [163,164]. However, enzymatic purification techniques 7106 L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114

(to eliminate those immunogenic telopeptides that induce foreign it may provide immunocompatible polymeric carriers for the deliv- body response) may be employed [172]. Alternatively, the use of ery of bioactive molecules and/or cells in various biomedical recombinant and non-recombinant human collagens can be envis- applications [101,102]. Polymerized fibrin is a major component aged but their production currently incurs high costs [164]. Colla- of blood clots and is recognized to play an important role in the gen is also difficult to process and its degradation rate cannot subsequent wound healing response [102,187]. On the other hand, easily be controlled [101,163]. For example, collagen degradability fibrin contains some specific domains that may improve cell bind- depends on cell three-dimensional structure penetration (which ing, and therefore it has also been studied as an advantageous bio- causes contraction, inner pressure increase, fluid restrictions and material for cell adhesion, spreading, migration, proliferation and makes collagen less swellable and degradable), and, in addition, tubule formation [101,153,187]. Due to these characteristics, fi- collagen is also degradable by other non-specific proteinases brin-based biomaterials (including modified/cross-linked fibrin [101]. Finally, collagen sterilization may be also an issue as the and fibrin composites) may also be applied for drug and cell deliv- sterilization methods currently employed may promote chemical ery for tissue engineering applications. The most widely used and physical modifications of the collagen structure [163]. forms of fibrin scaffolds are fibrin hydrogels and fibrin glue. Fibrin Gelatin is a collagen derivative which is commonly used as an hydrogels are known to promote angiogenesis and to enhance neu- hydrogel for pharmaceutical and biomedical applications mostly rite extension. A major drawback is that fibrin hydrogels have low because of its straightforward processability and good biodegrad- mechanical stiffness, and rapid degradation may occur before the ability/biocompatibility in physiological environments [101,173]. proper formation of tissue-engineered structures [187]. Finally, fi- Moreover, gelatin has relatively low antigenicity because it is a brin glues are biological adhesives commonly used in surgical pro- denatured protein material (in contrast to collagen, which is cedures (mostly due to their hemostatic, chemotactic and known to present some antigenicity due to its unaltered animal mitogenic properties) [101]. These glues have also been described origin) [102]. to facilitate the fixation of skin grafts and to limit the risk of infec- Gelatin can be obtained by the acidic or alkaline processing tion in chronic wounds [188]. Fibrin gels can be obtained by the (denaturation) of collagen [174]. Consequently, two different types enzymatic cross-linking of fibrinogen with thrombin. The final of gelatin can be obtained according to the methods employed for structure of fibrin gels will thus depend on the concentration of collagen pretreatment. These different pH pretreatments will also thrombin and fibrinogen, on local pH and ionic strength, as well affect the isoelectric points of the gelatin biomaterials obtained, as on the local calcium concentration [189]. Wound healing and manufacturers can now provide gelatin with a wide range of improvements were obtained after application of fibrin gels incor- isoelectric point values, from alkaline gelatin (with an isoelectric porating hematopoietic stem cells (CD34+), CD34+-derived endo- point of 9.0) down to acidic gelatin (with an isoelectric point of thelial cells, or both. Since pluripotent stem cells are able to 5.0) [101]. This is an important feature as it allows the complexa- differentiate into fibroblasts, keratinocytes and endothelial cells, tion of gelatin with either positively or negatively charged biomol- they may also play an important role during the wound healing ecules. Basic gelatin is preferable as the carrier matrix for an acidic process [189]. Bone marrow-derived stem cell transplantation bioactive molecule, while acidic gelatin should be employed for the can also be used for the healing of chronic lower extremity release of basic bioactive substances [175]. wounds. Hassan et al. [190] topically applied a concentrated solu- In general terms, the release of these substances is controlled by tion of bone marrow stem cells combined with platelets and fibrin the enzymatic degradation of the gelatin-based materials involved. glue in a collagen dressing. After 4 weeks of treatment, diabetic ul- Therefore, and similar to collagen, the degradation profiles (and the cers were totally closed in three patients and significantly reduced mechanical properties) of gelatin-based hydrogels may be adjusted in another five patients. Other approaches to enhance the effect of by controlling the degree of cross-linking (which will also control fibrin gels to improve healing include the use of enzymes to pro- the hydrogel water content) [176]. As for collagen cross-linking, duce and deliver nitric oxide (NO) which enhances the inflamma- it can be performed by chemical methods (e.g. using water-soluble tory response and faster re-epithelialization, and the use of carbodiimides [177], glutaraldehyde [178] or genipin [179])or platelets that work as powerful mitogenic and chemostatic factors. through physical cross-linking (by thermal treatment, by the for- The healing effect of Vivostat, a platelet-rich fibrin treatment for mation polyion complexes with other polymers or by blending DFUs, has been studied in a clinical trial [191]. The ulcers of pa- with other gelating polymers) [154,180]. tients were treated from weeks 1 to 6 with Vivostat platelet-rich Due to all the above-mentioned characteristics, collagen is fre- fibrin. The results showed that ulcers were completely healed after quently used to prepare wound dressing materials in diverse forms 12 weeks. These achievements are summarized in Table 2. that include gels, pads, particles, pastes, powders, sheets or solu- tions. A large number of commercial collagen-based dressings is al- 3.2.1.7. Silk fibroin. Fibroin protein can be isolated from the silk- ready available and some are specifically indicated for partial- and worm (Bombyx mori or Antheraea mylitta). It is receiving attention full-thickness pressure, venous, vascular and diabetic ulcers as is for biomedical applications due to its biocompatibility, hemocom- the case of BCGÒ, BIOSTEPÒ, CatrixÒ, CollaSorbÒ and PROMOGRAN patibility, slow degradability, water vapor and gas permeability be- PRISMAÒ Matrix (Table 3). sides its widespread versatility [192,193]. Silk fibers are composed As reported in Table 2, recent studies have proved the efficacy of a fibrous protein (fibroin) core and a glue protein (sericin) sur- of collagen and gelatin dressings for decreasing infection by bacte- rounding it. Even though fibroin does not promote immunological ria and favoring granular tissue formation, stimulating faster responses, silk sericin protein may have the opposite effect [194]. wound healing in DFU patients [181–184]. Different approaches In addition, silk fibroin is able to support epidermal cells and fibro- tested so far include the incorporation of glucose oxidase in a col- blast attachment, spreading and proliferation, thus promoting lagen matrix in order to achieve the sustained delivery of reactive wound healing [101]. Fibroin films loaded with aloe gel extract oxygen species (ROS), natural compounds (such as polyphenols), were recently applied in the treatment of streptozotocin-induced growth factors (such as bFGF), antibiotics (such as doxycycline diabetic rats [193]. Compared to aloe-free fibroin film, the blended and levofloxacin) and ionic silver as antimicrobial agent film enhanced the attachment and the proliferation of skin fibro- [182,185,186]. blasts. Moreover the wounds in diabetic rats presented a smaller area 7 days after wounding (when compared to untreated diabetic 3.2.1.6. Fibrin. Fibrin is a protein that is produced from fibrinogen wounds) and fibroblast distribution and collagen fiber organization and hence can be autologously harvested from patients. Therefore, similar to wounds in normal rats. These results show that acceler- L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114 7107 ated wound healing can be obtained by using blended fibroin/aloe and physical properties [173]. The risks of biological contamination gel films which may be applied in the treatment of diabetic non- are non-existent. In addition, some of these synthetic polymers are healing skin ulcers. mainly degraded via chemical hydrolysis and are quite insensitive to a number enzymatic processes, and hence their degradation 3.2.1.8. Dextran. Dextran is constituted by a(1?6)-linked D-glu- behavior will not vary greatly from patient to patient [173]. Syn- cose residues with some degree of branching via a(1?3) linkages, thetic polymers that are being used for the development of wound and is obtained from various bacterial strains via the action of dex- dressings, in particular those that can be used for DFU treatment, transucrase [101,141]. Dextran is hydrophilic, highly soluble in will be presented and discussed in the following section. water, inert in biological systems and easily functionalized through its reactive hydroxyl groups [195,196]. Dextran is available in a 3.2.2.1. Poly(vinyl alcohol) (PVA). PVA is a hydrophilic, non-toxic, wide range of molecular weights, as well as in the form of several non-carcinogenic, biocompatible polymer obtained from vinyl ace- dextran derivatives. It is biodegradable, biocompatible, resists pro- tate by alcoholysis, hydrolysis or aminolysis [61,80,153]. PVA has tein adsorption and does not affect cell viability. Therefore it is a been widely used for tissue engineering and drug delivery applica- good polymer for medical applications such as bone, dermal and tions, and besides its high hydrophilicity and water absorption subcutaneous healing and for drug delivery [101,196]. It facilitates capacity, it also presents an excellent capacity to be processed in inflammatory cell infiltration and promotes angiogenic cell migra- the form of particles, fibers, textiles, sponges and films. Further- tion into the wounds [197]. Diabetic patients have been treated more, it presents good chemical/enzymatic resistance, as well as with dextranomer, a dextran polymer which is applied locally to good mucoadhesive and oxygen permeability properties [207– the ulcer or the infected wound [198]. Wounds were covered with 209]. However, PVA exhibits some unfavorable mechanical a thick layer of dextranomer and further covered with a dry absor- properties (e.g. strength and flexibility), as well as a relatively poor bent gauze and non-occlusive bandage dressing. Of the 15 lesions thermal stability [210], though this can be improved by blending treated, 12 healed completely (for an average period of 8 days) PVA with other polymers (including naturally based polymers such showing the potential of dextran-based materials to treat DFUs. as chitosan, gelatin, dextran and hyaluronic acid) [211–213] or by This study showed that the effect of dextranomer on the infected adequate chemical or physical cross-linking [61,208]. Chemical wound was rapid, leading to a remarkable decrease of the inflam- cross-linking can be obtained by using glutaraldehyde, genipin, matory reaction around the wound during the first day and the for- succinyl chloride, adipoyl chloride and sebacoyl chloride, while mation of healthy granulation tissue within a few days without physical cross-linking can be obtained by repeated freeze–thawing pain, edema and tenderness. According to this and other previous cycles [61,209,214]. PVA is not chemically or enzymatically studies it was proposed that the enhanced effect of dextranomer degradable in vivo but it may erode quite easily (by dissolution) is due to its capacity to cleanse the lesion by absorbing the wound and thus may not be useful as a long-term or permanent dressing exudate, protein degradation products, prostaglandins, bacteria [153]. and other contaminants, reducing inflammation and improving PVA and its derivatives have already been used as wound dress- healing. ings for conventional wounds, and have also been tested for dia- betic wound treatments [215]. Enhanced healing results were 3.2.1.9. Elastin. Elastin is an insoluble ECM protein and a major obtained by incorporating NO into the PVA dressing since exoge- constituent of skin elastic fibers [199,200]. Elastin is highly insolu- nous NO released increased collagen production, enhanced the ble and difficult to process into new biomaterials. Nevertheless, its quality of the granulation tissue and increased the wound strength. soluble forms, including tropoelastin (a soluble precursor form of PVA has also been cross-linked with sodium carboxymethylcellu- elastin), a-elastin (an oxalic acid derivative of elastin) and elas- lose and dextran to improve PVA water (and consequently exu- tin-like polypeptides have much broader applications as elastin- date) swelling capacity as well as its water vapor transmission based biomaterials [200,201]. Elastin can also be cross-linked by rate. Besides NO, PVA-based dressings have also been loaded with chemical (e.g. using aldehydes and epoxy groups) [202,203], enzy- bioactive compounds such as gentamicin and ciprofloxacin since matic [204] and physical processes [205]. These strategies allow an the efficient release of anti-bacterial drugs may help to improve efficient binding to amino acids side chains, low antigenicity and complications in long-term healing [215,216]. improved mechanical strength [201]. Soluble elastin-based bioma- terials promote a natural elasticity, favorable cellular interactions and enhanced tissue regeneration through increased chemotactic 3.2.2.2. Poly(ethylene glycol) (PEG)/Poly(ethylene oxide) (PEO). PEG is activity, fibroblast proliferation and collagenase synthesis [206]. a polyether which is also known as poly(ethylene oxide) (PEO) or Despite the scarcity of reports concerning the application of elas- as poly(oxyethylene) (POE), depending on its molecular weight tin-based dressings to DFU treatments, a recent study demon- [80]. It is a hydrophilic, biocompatible, flexible, non-toxic and strated that a protein gel comprised of elastin-like peptides non-immunogenic material that is resistant to protein adsorption loaded with keratinocyte growth factor (KGF) enhanced the re-epi- and can be synthesized by anionic or cationic polymerization of thelialization and granulation of wounds in diabetic mice [199], ethylene oxide [80,153,217]. indicating that elastin can be considered an interesting naturally PEG presents almost all of the favorable and unfavorable prop- based polymeric material for enhancing DFU healing. erties of PVA when wound dressing applications are envisaged [218]. Furthermore, its terminal hydroxyl groups can be deriva- 3.2.2. DFU dressings based on synthetic polymers tized to create PEG macromers that can participate in other chain Due to the large number of available chemical monomeric enti- or step polymerizations. PEG macromers have low toxicity, and ties of potential interest and due to the recent advances in polymer can be coupled with peptides or growth factors and placed synthesis and processing methods, many new synthetic biocom- in situ to fill irregular sites [80,217]. Three major cross-linking patible, biodegradable/non-biodegradable polymers and copoly- methods have been used to prepare PEG-based hydrogels: radia- mers have been developed in recent years [195]. Some of these tion of linear or branched PEG polymers [219]; free radical poly- polymeric materials can overcome the problems typically associ- merization of PEG acrylates [220]; and other specific chemical ated with natural polymers as they can be synthesized and pro- reactions, such as condensation reactions [220], Michael-type cessed in a highly controlled way, thus leading to homogeneous additions [221] and enzymatic reactions [222]. PEG acrylates such materials that will present constant and reproducible chemical as PEG diacrylate, PEG dimethacrylate and multiarm PEG (n-PEG) 7108 L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114 acyrlate are the major types of macromers used for photopolymer- PU-derived materials (mainly in the form of films or foams) in mul- ization [217]. tilayer dressings in order to optimize their healing capacity. As an PEG can also be blended with other polymers such as chitosan, example, the commercial wound dressing MeliplexÒ Ag (Mol- poly(lactic-co-glycolic acid) (PLGA) and poly(propylene fumarate) nlycke Health Care, Sweden) comprises a silicone wound contact (PPF) in order to improve its inherent solubility, erosion, mechan- layer, an absorbent material (polyurethane foam pad), an anti-bac- ical and thermal properties as well as its crystallinity and viscosity terial (a silver compound, silver sulfate) and a vapor-permeable [218,223]. The formation of PEG-based block copolymers is also a waterproof film to absorb exudate and to maintain a moist wound viable option. PEG-based hydrogels have been used for many bio- environment. It can be used on exuding wounds at risk of infection medical applications including wound dressings [218,224]. In addi- such as leg ulcers, DFUs, pressure ulcers and burns [243]. As dis- tion, this type of hydrogel has already been demonstrated to be cussed before, PU-based dressings have also been loaded with bio- advantageous for diabetic wounds as it promotes proliferation of active compounds to shorten healing periods. A wound dressing skin cells, enhanced collagen deposition and reduced scar forma- containing an antimicrobial therapeutic agent (e.g. penicillin, tion [225–228]. As in the case of the previously discussed materi- erythromycin, chlorohexidine, triclosan), a pain-relieving sub- als, PEG has also been associated with other polymers such as PCL, stance (e.g. ibuprofen) and protease inhibitors (e.g. MMP-9, elas- and can be loaded with growth factors such as EGF, bFGF, pbFGF or tase, MMP-8, MMP-12) in a barrier layer made of collagen/ rhaFGF which help to increase the wound recovery rate, leading to polylactide/polyglycolide or polyurethane was recently patented improved vascularization, enhanced collagen deposition, and mat- [238]. This layer breaks down in contact with wounds, releasing uration and complete re-epithelialization [226,227,229,230]. the therapeutic substances into the wound. This invention was developed for chronic wound treatment, such as venous ulcers or 3.2.2.3. Poly(vinyl pyrrolidone) (PVP). Like PVA and PEG, this hydro- DFUs. These and other examples are summarized in Table 2. philic and biocompatible material has been extensively used for a wide variety of pharmaceutical and biomedical applications 3.2.2.5. Poly (hydroxyethyl methacrylate) (PHEMA). PHEMA-based (including wound dressings). This is mostly due to its water polymers and copolymers are important biocompatible, non-bio- absorption and oxygen permeability properties [231,232]. PVP degradable materials that can lead to the formation of hydrogels hydrogels can be produced at relatively low cost. This process is to be employed in various different biomedical and pharmaceutical simple, safe and efficient [218,233]. Like the two above-described applications [244]. Their final chemical, physical, sorption and per- hydrophilic synthetic polymers (i.e. PVA and PEG), PVP is usually meability properties will depend on the synthesis method and con- blended with other polymers (e.g. agar, cellulose or PEG) or ditions, on the chemical nature and proportions of the employed cross-linked with carbodiimides in order to modify its solubility, co-monomers and cross-linkers, as well as on the final degree of delivery and erosion profiles, mechanical properties, softness and cross-linking [218]. PHEMA-based polymers usually present good elasticity [218]. A significant improvement in wound healing of oxygen permeability, good water sorption and transmission rates, diabetic rats was achieved after application of a new NO delivery high biocompatibility and non-toxicity [244,245]. PHEMA-based platform based on grafting S-nitrosothiols, derived from endoge- hydrogels have been used for artificial skin manufacturing and nous glutathione (GSH) or its oligomeric derivatives, phytochela- wound dressing applications [153,218] and many bioactive sub- tins, onto poly(vinyl methyl ether co-maleic anhydride) and the stances have been incorporated into these materials [153].An subsequent formation of interpolymer complexes with PVP. This interesting example is the case of a hybrid dressing consisting of complex provides controlled release of NO for more than 10 days, a pHEMA core (containing a light-activated NO donor) and a PU and a single topical application of the NO-controlled delivery sys- coating for use on chronic wounds [246]. One major advantage of tem accelerates wound closure as compared with the control [234]. this material is the fact that NO release can be controlled by light These results suggested that NO-releasing interpolymer complexes exposure. The dressing can be illuminated from time to time to de- could be potentially useful for diabetic wound healing. liver NO only to the wound site, maintaining antiseptic conditions. This approach might be superior to simple washing of the affected 3.2.2.4. Polyurethanes (PUs). Polyurethanes are synthesized by con- area with conventional solutions such as hydrogen peroxide. densation and polymerization methods from a wide range of PHEMA and PEG have been combined to develop a hydrogel bifunctional or higher-order functional monomers. This will lead dressing that can bind covalently to MMP inhibitors and promote to versatile polymeric materials that may present quite different the healing of chronic wounds as DFUs. This patented dressing en- chemical, physical and biological properties [235], such as hydro- sures that MMPs in the chronic wound fluid are inhibited (thus philic/hydrophobic characteristics, water sorption, permeation reducing their proteolytic content) while guaranteeing that the and degradation profiles, as well as thermal and mechanical prop- necessary MMP levels for normal healing are not affected in the erties [236]. As an example, PUs can lead to hard, flexible or elas- wound bed [247]. tomeric materials, even without covalent cross-linking [237]. PUs are also non-toxic, sterilizable, non-adherent and non-allergenic 3.2.2.6. Poly (a-esters) (PLA, PGA, PLGA, PCL). Polylactide (PLA) is one [238]. Furthermore, PUs may be easily cross-linked, blended with of the most popular aliphatic polyesters since it presents relatively other synthetic and/or natural-based polymers, and processed in high strength and an appropriate degradation rate for most drug the form of particles, fibers, films, foams and hydrogels [239]. delivery and tissue engineering systems [248]. In fact, PLA pos- PU-based nanofibers showed controlled evaporative water loss sesses good mechanical characteristics, controlled degradability and promoted wound fluid drainage, which are essential character- and excellent biocompatibility. However, its strong hydrophobicity istics for wound dressing materials [240,241]. When compared to limits some of its potential applications [248–250]. other conventional dressings, some PU-based foam dressings Polyglycolic acid (PGA) is another poly(a-ester) that presents a showed higher healing capacities [237,238,241,242]. A dressing relatively hydrophilic nature and degrades faster than PLA in aque- constituted of polymeric fibers with repeated units containing ure- ous solutions or in vivo. To obtain intermediate degradation rates thane groups (aliphatic polyurethane, aromatic polyurethane, ali- between PGA and PLA, several copolymers of lactic acid and of gly- phatic polyurethane, aromatic polyurethane or a combination of colic acid poly(lactic-co-glycolic acid) (PLGA) can be synthesized them) was recently patented and presented as effective for the [250,251]. treatment of chronic wounds such as DFUs [237]. The improved PLGA is also a biodegradable polymer with strong biocompati- capacity to manage wound exudates justifies the regular use of bility, controlled biodegradability and potential for sustained re- L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114 7109 lease of various bioactive substances [252]. Furthermore, it can be alleviate pain, to deliver drugs and to reduce odors. The necessity processed into many different forms—powder, pellets, fibers, nano- to develop and improve the efficacy of wound dressings, particles, etc. PLGA microspheres loaded with rhEGF were demon- particularly suitable for DFU treatment, has been a challenge for strated to enhance the growth rate of fibroblasts, and it was also both researchers and clinicians. An ideal dressing should confer observed that wounds in diabetic rats healed more efficiently than moisture balance, protease sequestration, growth factor stimula- when pure rhEGF is used [252,253]. tion, antimicrobial activity, oxygen permeability and capacity to Dong et al. [252] prepared PLGA microspheres loaded with rhE- promote autolytic debridement that facilitates the production of GF by a solvent-evaporation technique. These microspheres were granulation tissue and the re-epithelialization process. In addition, small in size and presented a high drug encapsulation capacity it should have a prolonged time of action, high efficiency and im- (86%). Furthermore, rhEGF-loaded microspheres loaded into the proved sustained drug release in the case of medicated systems. wound site enhanced the growth rate of fibroblasts, and it was also New and recent alternatives to conventional dressings have observed that wounds in diabetic rats healed more efficiently than been developed; these include mixing different polymers and when pure rhEGF is used. Chu et al. [253] used a modified double- using more efficient cross-linking methods to create improved emulsion method to prepare rhEGF-loaded PLGA nanoparticles to materials that guarantee an optimal wound environment. As dis- heal diabetic ulcers. In diabetic rats, these rhEGF-loaded nanopar- cussed, natural (chitosan, hyaluronic acid, cellulose, alginate, colla- ticles promoted a faster healing rate as well as fibroblast gen, fibrin) or synthetic (PVA, PEG, PVP, PU, PHEMA, poly(a- proliferation. esters)) polymers have been combined or cross-linked (e.g. with These copolymers can be applied in skin tissue regeneration genipin, oxidized dextran or glutaraldehyde) for this purpose. Fur- and suture applications, and have been approved by the FDA for thermore, medicated dressings have been examined as a means to several biomedical and pharmaceutical applications [250]. The efficiently deliver drugs or other bioactive substances that had pre- incorporation of drugs and other bioactive substances into viously been demonstrated to improve DFU treatment. Dressings poly(a-hydroxy acids) has been done with DFU applications in loaded with antimicrobials/antibiotics (to decrease infection), mind. Xu et al. [254] reported the incorporation of a hydrophilic platelet-derived substances, patients’ own stem cells, growth fac- antibiotic drug, tetracycline hydrochloride (TCH), into an electro- tors and peptides act to balance (through up-regulation of growth spun PEG–PLA nanofibrous membrane. This drug-impregnated factors and cytokines and down-regulation of destructive proteol- membrane demonstrated sustained release of TCH over 6 days ysis) the biochemical events of inflammation in the chronic wound and was effective at inhibiting growth of Staphylococcus aureus. and to improve healing. Some studies dealing with the incorpora- As observed before for other polymer-based dressings, the loading tion of natural extracts showed great potential in the treatment of of growth factors into PLA-based materials to stimulate the wound DFUs; however, these findings do not yet represent a practical op- healing process is also an option for DFU treatment. As an example, tion since application of these compounds tends be very expensive bFGF was embedded into ultrafine PLA fibers with a core–sheet and difficult to regulate/control. Therefore, and in the near future, structure [99]. An initially low burst release was achieved, fol- research will certainly focus on the development of more efficient lowed by controlled release for around 4 weeks, a profile that is and less expensive biocompatible and biodegradable medicated interesting for application in chronic wounds. Results also showed dressings that can deliver important DFU healing factors to the a higher wound recovery rate with complete re-epithelialization, wound site in order to improve patient care and quality of life. regeneration of skin appendages, higher density and mature capil- lary vessels in bFGF-loaded scaffolds when compared with fibers Acknowledgements without bFGF and after 2 weeks of treatment. Moreover, it also presented enhanced collagen deposition, an ECM remodeling pro- This work was financially supported by COMPETE and Fundação cess and components of collagen fibers similar to normal tissues. para a Ciência e Tecnologia (FCT-MES) under contracts, PTDC/SAU- Polycaprolactone (PCL) is another biodegradable and biocom- BEB/71395/2006, PTDC/SAU-MII/098567/2008, PTDC/SAU-FAR/ patible poly(a-ester) which has been studied for tissue regenera- 121109/2010, PEst-C/SAU/LA0001/2011, by EFSD/JDRF/Novo Nor- tion and wound healing applications since it promotes a faster disk European Programme in Type 1 Diabetes Research and Socied- healing and reduced inflammatory infiltrate [255]. However, PCL ade Portuguesa de Diabetologia. L.I.F.M. and A.M.A.D. acknowledge degrades at a significantly slower rate than PLA, PGA and PLGA FCT-MES for their fellowships SFRH/BD/60837/2009 and SFRH/ [256]. This slow degradation makes PCL less attractive for this type BPD/40409/2007, respectively. of biomedical application, but more attractive for sutures, long- term implants and controlled-release applications [250]. Merrel et al. [255] developed PCL nanofibers as a delivery vehi- Appendix A. Figures with essential colour discrimination cle for curcumin for diabetic wound healing applications [255]. Curcumin is a natural phenolic compound with anti-oxidant and Certain figures in this article, particularly Figures 2 and 3, are anti-inflammatory properties. The prepared curcumin-loaded difficult to interpret in black and white. The full colour images nanofibers reduced inflammatory induction from mouse mono- can be found in the on-line version, at http://dx.doi.org/10.1016/ cyte–macrophages. In addition they increased the rate of wound j.actbio.2013.03.033. closure in a STZ-induced diabetic mouse model. These results dem- onstrated that these curcumin-loaded PCL nanofibers are bioactive References and have potential to be applied as wound dressings with anti-oxi- dant and anti-inflammatory properties for DFU treatment. [1] Shaw JE, Sicree RA, Zimmet PZ. Global estimates of the prevalence of diabetes for 2010 and 2030. Diabetes Res Clin Pract 2010;87:4–14. [2] Whiting DR, Guariguata L, Weil C, Shaw J. IDF Diabetes Atlas: global estimates of the prevalence of diabetes for 2011 and 2030. Diabetes Res Clin Pract 4. Future trends and perspectives 2011;84:311–21. [3] Chittleborough CR, Grant JF, Phillips PJ, Taylor AW. The increasing prevalence of diabetes in South Australia: the relationship with population ageing and DFUs are a frequent complication of diabetes that may lead to obesity. Public Health 2007;121:92–9. severe and persistent infection and, in extreme cases, to lower- [4] Ahmed I, Glodstein B. Diabetes mellitus. Clin Dermatol 2006;24:237–46. [5] Daneman D. Type 1 diabetes. Lancet 2006;367:847–58. extremity amputation. Therapeutics usually involves the use of [6] Vehik K, Dabelea D. The changing epidemiology of type 1 diabetes: why is it dressings, aiming to enhance the life quality of DFU patients, to going through the roof? Diabetes Metab Res Rev 2011;27:3–13. 7110 L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114

[7] Wang J, Luben R, Khaw KT, Bingham S, Wareham NJ, Forouhi NG. Dietary [37] Monaco JL, Lawrence WT. Acute wound healing: and overview. Clin Plast Surg energy density predicts the risk of incident type 2 diabetes: the European 2003;30:1–12. Prospective Investigation of Cancer (EPIC)-Norfolk Study. Diabetes Care [38] Singer AJ, Clark RA. Cutaneous wound healing. N Engl J Med 2008;31:2120–5. 1999;341:738–46. [8] Knowler WC, Barrett-Connor E, Fowler SE, Hamman RF, Lachin JM, Walker EA, [39] Rodero MP, Khosrotehrani K. Skin wound healing modulation by et al. Reduction in the incidence of type 2 diabetes with lifestyle intervention macrophages. Int J Clin Exp Pathol 2010;3:643–53. or metformin. N Engl J Med 2002;346:393–403. [40] Wilgus TA. Immune cells in the healing skin wound: influential players at [9] Kahn SE. The relative contributions of insulin resistance and beta-cell each stage of repair. Pharmacol Res 2008;58:112–6. dysfunction in the pathophysiology of type 2 diabetes. Diabetologia [41] Tsirogianni AK, Moutsopoulos NM, Moutsopoulos HM. Wound healing: 2008;46:3–19. immunological aspects. Injury 2006;37:S5–S22. [10] McCance DR. Pregnancy and diabetes. Best Pract Res Clin Endocrinol Metab [42] Schreml S, Szeimies R, Prantl L, Landthaler M, Babilas P. Wound healing in 2011;25:945–58. 21st century. J Am Acad Dermatol 2010;63:866–81. [11] Kim C, Newton KM, Knopp RH. Gestational diabetes and the incidence of type [43] Tellechea A, Leal E, Veves A, Carvalho E. Inflammatory and angiogenic 2 diabetes: a systematic review. Diabetes Care 2002;25:1862–8. abnormalities in diabetic wound healing: role of neuropeptides and [12] Ali S, Dornhorst A. Diabetes in pregnancy: health risks and management. therapeutic perspectives. Open Circ Vasc J 2009;3:43–55. Postgrad Med J 2011;57:417–27. [44] Basic-Kes V, Zavoreo I, Rotim K, Bornstein N, Rundek T, Demarin V. [13] Vague J, Vague P, Tramoni M, Vialette B. Obesity and diabetes. Acta Diabetol Recommendations for diabetic polyneuropathy treatment. Acta Clin Croat 1980;17:87–9. 2011;50:289–302. [14] Mokdad A, Ford E, Bowman B. Prevalence of obesity, diabetes and obesity- [45] Aring AM, Jones DE, Falko JM. Evaluation and prevention of diabetic related health risk factors. J Am Med Assoc 2003;289:76–9. neuropathy. Am Fam Physician 2005;71:2123–8. [15] Haslam D. Obesity and diabetes: the links and common approaches. Prim [46] Vinik A, Ullal J, Parson HK, Casellini CM. Diabetic neuropathies: clinical Care Diab 2010;4:105–12. manifestions and current treatment options. Nat Rev Endocrinol 2006;2: [16] Schamseddeen H, Getty JZ, Hamdallah IN, Ali MR. Epidemiology and 269–81. economic impact of obesity and Type 2 diabetes. Surg Clin North Am [47] Boulton AJ, Malik RA, Arezzo JC, Sosenko JM. Diabetic somatic neuropathies. 2011;91:1163–72. Diabetes Care 2004;27:1458–86. [17] Fontbonne A, Eschwege E, Cambien F, Richard JL, Ducimetiere P, Thibult N, [48] Rathur HM, Bloulton AJM. Recent advances in the diagnosis and management et al. Hypertriglyceridaemia as a risk factor of coronary heart disease of diabetic neuropathy. J Bone Joint Surg 2005;87:1605–10. mortality in subjects with impaired glucose tolerance or diabetes. Results [49] Snyder BJ, Waldman BJ. Venous thromboembolism prophylaxis and wound from the 11-year follow-up of the Paris Prospective Study. Diabetologia healing in patients undergoing major orthopedic surgery. Adv Skin Wound 1989;32:300–4. Care 2009;22:311–5. [18] Srikanth S, Deedwania P. Primary and secondary prevention strategy for [50] Lobmann R, Zemlin C, Motzkau M, Reschke K, Lehnert H. Expression of cardiovascular disease in diabetes mellitus. Cardiovasc Clin 2011;29:47–70. matrix metalloproteinases and growth factors in diabetic foot wounds [19] Gimenez M, Lopez JJ, Castell C, Conget I. Hypoglycaemia and cardiovascular treated with a protease absorbent dressing. J Diabetes Complications disease in Type 1 Diabetes. Results from the Catalan National Public Health 2006;20:329–35. registry on insulin pump therapy. Diabetes Res Clin Pract 2012;96:e23–5. [51] Liu Y, Min D, Bolton T, Nube V, Twigg SM, Yue DK, et al. Increased Matrix [20] Andersen AR, Christiansen JS, Andersen JK, Kreiner S, Deckert T. Diabetic Mettaloproteinase-9 predicts poor wound healing in diabetic foot ulcers. nephropathy in type 1 (insulin-dependent) diabetes: an epidemiological Diabetes Care 2009;32:e137. study. Diabetologia 1983;25:496–501. [52] Guo S, Dipietro LA. Factors affecting wound healing. J Dent Res 2010;89: [21] Mogensen CE, Christensen CK. Predicting diabetic nephropathy in insulin- 219–29. dependent patients. N Engl J Med 1984;311:89–93. [53] Acosta JB, del Barco DG, Vera DC, Savigne W, Lopez-Saura P, Guillen Nieto G, [22] Mohammedi K, Maimaitiming S, Emery N, Bellili-Munõz N, Roussel R, et al. The pro-inflammatory environment in recalcitrant diabetic foot Fumeron F, et al. Allelic variations in superoxide dismutase-1 (SOD1) gene wounds. Int Wound J 2008;5:530–9. are associated with increased risk of diabetic nephropathy in type 1 diabetic [54] Blakytny R, Jude EB. Altered molecular mechanisms of diabetic foot ulcers. Int subjects. Mol Genet Metab 2011;104:654–60. J Low Extrem Wounds 2009;8:95–104. [23] Zhang S, Zhang Y, Wei X, Zhen J, Wang Z, Li M, et al. Expression and regulation [55] Bloomgarden ZT. The diabetic foot. Diabetes Care 2008;31:372–6. of a novel identified TNFAIP8 family is associated with diabetic nephropathy. [56] Brem H, Tomic-Canic M. Cellular and molecular basis of wound healing in BBA Mol Basis Dis 2010;1802:1078–86. diabetes. J Clin Invest 2007;117:1219–22. [24] Leibowitz HM, Krueger DE, Maunder LR, Milton RC, Kini MM, Kahn HA, et al. [57] Muller M, Trocme C, Lardy B, Morel F, Halimi S, Benhamou PY. Matrix The Framingham Eye Study monograph: An ophthalmological and metalloproteinases and diabetic foot ulcers: the ratio of MMP-1 to TIMP-1 is a epidemiological study of cataract, glaucoma, diabetic retinopathy, macular predictor of wound healing. Diab Med 2008;25:419–26. degeneration, and visual acuity in a general population of 2631 adults, 1973– [58] Pradhan l, Nabzdyk C, Andersen N, LoGerfo F, Veves A. Inflammation and 1975. Surv Ophthalmol 1980;24:335–610. neuropeptides: the connection in diabetic wound healing. Expert Reviews in [25] Klein R, Klein BE, Moss SE, Davis MD, DeMets DL. The Wisconsin Molecular Medicine 2009;11:1–24. epidemiologic study of diabetic retinopathy. III. Prevalence and risk of [59] O’Loughlin A, O’Brien T. Topical stem and progenitor cell therapy for diabetic diabetic retinopathy when age at diagnosis is 30 or more years. Arch foot ulcers. Stem Cells Clin Res 2011;978:579–604. Ophthalmol 1984;102:527–32. [60] Mulder G, Armstrong D, Seaman S. Diabetic foot ulcerations: dressings. [26] Kim BY, Kim CH, Jung CH, Mok JO, Suh KI, Kang SK. Association between Wounds 2003;15:4–15. subclinical hypothyroidism and severe diabetic retinopathy in Korean [61] Jannesari M, Varshosaz J, Morshed M, Zamani M. Composite poly(vinyl patients with type 2 diabetes. Endocr J 2011;58:1065–70. alcohol)/poly(vinyl acetate) electrospun nanofibrous mats as a novel wound [27] Chen H, Zheng Z, Huang Y, Guo K, Lu J, Zhang L, et al. A microalbuminuria dressing matrix for controlled release of drugs. Int J Nanomed threshold to predict the risk for the development of diabetic retinopathy in 2011;6:993–1003. type 2 diabetes mellitus patients. PLoS ONE 2012;7:e36718. [62] Cavanagh PR, Lipsky BA, Bradbury AW, Botek G. Treatment for diabetic foot [28] Brown MJ, Martin JR, Asbury AK. Painful diabetic neuropathy. A ulcers. Lancet 2005;366:1725–35. morphometric study. Arch Neurol 1976;33:164–71. [63] Leung PC. Diabetic foot ulcers—a comprehensive review. Surgeon 2007;5: [29] Dyck PJ, Kratz KM, Karnes JL, Litchy WJ, Klein R, Pach JM, et al. The prevalence 219–31. by staged severity of various types of diabetic neuropathy, retinopathy, and [64] Oyibo SO, Jude EB, Tarawneh I, Nguyen HC, Harkless LB, Boulton AJM. A nephropathy in a population-based cohort: the Rochester Diabetic comparison of two diabetic foot ulcer classification systems: the Wagner and Neuropathy Study. Neurology 1993;43:817–24. the University of Texas wound classification systems. Diabetes Care [30] Silva L, Carvalho E, Cruz MT. Role of neuropeptides in skin inflammation and 2001;24:84–8. its involvement in diabetic wound healing. Expert Opin Biol Ther [65] O´ Donnell TF, Lau J. A systematic review of randomized controlled trials of 2010;10:1427–39. wound dressings for chronic venous ulcer. Journal of Vascular Surgery [31] Kim SK, Lee KJ, Hahm JR, Lee SM, Jung TS, Jung JH, et al. Clinical significance of 2006;44:1118–25. the presence of autonomic and vestibular dysfunction in diabetic patients [66] Morin RJ, Tomaselli NL. Interactive dressings and topical agents. Clin Plast with peripheral neuropathy. Diab Metab J 2012;36:64–9. Surg 2007;34:643–58. [32] Enoch S, Leaper DJ. Basic science of wound healing. Surgery 2008;26:31–7. [67] Lloyd LL, Kennedy JK, Methacanon P, Paterson M, Knill CJ. Carbohydrate [33] Li J, Chen J, Kirsner R. Pathophysiology of acute wound healing. Clin Dermatol polymers as wound management aids. Carbohydr Polym 1998;37: 2007;25:9–18. 315–22. [34] Sidhu GS, Mani H, Gaddipati JP, Singh AK, Seth P, Banaudha KK, et al. [68] Mulder M. The selection of wound care products for wound bed preparation. Curcumin enhances wound healing in streptozotocin induced diabetic rats Prof Nurs Today 2011;30:15–21. and genetically diabetic mice. Wound repair and regeneration: official [69] Harding KG, Jones V, Price P. Topical treatment: which dressing to choose. publication of the Wound Healing Society [and] the European Tissue Repair Diabetes Metab Res Rev 2000;16(Suppl. 1):S47–50. Society 1999;7:362–74. [70] Morton LM, Phillips TJ. Wound healing update. Semin Cutan Med Surg [35] Falanga V. Wound healing and its impairment in the diabetic foot. Lancet 2012;31:33–7. 2005;366:1736–43. [71] Wittaya-areekul S, Prahsarn C. Development and in vitro evaluation of [36] Delavary BM, Veer WM, Egmond M, Niessen FB, Beelen RHJ. Macrophages in chitosan-polysaccharides composite wound dressings. Int J Pharm skin injury and repair. Immunobiology 2011;216:753–62. 2006;313:123–8. L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114 7111

[72] Boateng JS, Matthews KH, Stevens HN, Eccleston GM. Wound healing [105] Dai T, Tanaka M, Huang YY, Hamblin MR. Chitosan preparations for wounds dressings and drug delivery systems: a review. J Pharm Sci 2008;97: and burns: antimicrobial and wound-healing effects. Expert Rev Anti Infect 2892–923. Ther 2011;9:857–79. [73] Fonder MA, Lazarus GS, Cowan DA, Aronson-Cook B, Kohli AR, Mamelak AJ. [106] Khoushab F, Yamabhai M. Chitin research revisited. Mar Drugs Treating the chronic wound: a practical approach to the care of 2010;8:1988–2012. nonhealing wounds and wound care dressings. J Am Acad Dermatol [107] Madihally SV. Processing chitosan for tissue regeneration. Curr Trends Polym 2008;58:185–206. Sci 2011;15:83–8. [74] Hilton JR, Williams DT, Beuker B, Miller DR, Harding KG. Wound dressings in [108] Koide SS. Chitin-chitosan: properties, benefits and risks. Nutr Res diabetic foot disease. Clin Infect Dis 2004;39(Suppl. 2):S100–3. 1998;13:1091–101. [75] Fletcher J, Moore Z, Anderson I, Matsuzaki K. Pressure ulcers and [109] Kim IY, Seo SJ, Moon HS, Yoo MK, Park IY, Kim BC, et al. Chitosan and its hydrocolloids. Wound Int 2011;2:1–6. derivatives for tissue engineering applications. Biotechnol Adv [76] Dumville JC, Deshpande S, O’Meara S, Speak K. Hydrocolloid dressings for 2008;26:1–21. healing diabetic foot ulcers. Cochrane Database Syst Rev 2012;2:CD009099. [110] Jayakumar R, Prabaharan M, Nair SV, Tamura H. Novel chitin and chitosan [77] Jeffcoate WJ, Price P, Harding KG. Wound healing and treatments for people nanofibers in biomedical applications. Biotechnol Adv 2010;28:142–50. with diabetic foot ulcers. Diabetes Metab Res Rev 2004;20(Suppl. 1):S78–89. [111] Dash M, Chiellini F, Ottenbrite RM, Chiellini E. Chitosan—a versatile semi- [78] McIntosh C. Are hydrocolloid dressings suitable for diabetic foot ulcers? synthetic polymer in biomedical. Progress in Polymer Science 2011;678. Wound Essent 2007;2:170–2. [112] Rinaudo M. Chitin and chitosan: properties and applications. Prog Polym Sci [79] Dumville JC, Soares MO, O’Meara S, Cullum N. Systematic review and mixed 2006;31:603–32. treatment comparison: dressings to heal diabetic foot ulcers. Diabetologia [113] Chatelet C, Damour O, Domard A. Influence of the degree of acetylation on 2012;55:1902–10. some biological properties of chitosan films. Biomaterials 2001;22:261–8. [80] Slaughter BV, Shahana SK, Fisher OZ, Khademhosseini A, Peppas NA. [114] Pérez RA, Won J, Knowles JC, Kim H. Naturally and synthetic smart composite Hydrogels in regenerative medicine. Adv Mater 2009;21:3307–29. biomaterials for tissue regeneration. Advanced Drug Delivery Reviews 2012. [81] Edwards J, Stapley S. Debridment of diabetic foot ulcers. Cochrane Database [115] Tan Y, Han F, Ma S, Yu W. Carboxymethyl chitosan prevents formation of Syst Rev 2010;20:1–44. broad-spectrum biofilm. Carbohydr Polym 2011;84:1365–70. [82] Skorkowska-Telichowska K, Czemplik M, Kulma A, Szopa J. The local [116] Santos KSCR, Silva HSRC, Ferreira EI, Bruns RE. 32 Factorial design and treatment and available dressings for chronic wounds. J Am Acad Dermatol response surfasse analysis optimization of N-carboxybutylchitosan synthesis. 2011;5:1–11. Carbohydr Polym 2005;59:37–42. [83] Weller C, Sussman G. Wound dressings update. J Pharm Pract Res [117] Dias AM, Seabra IJ, Braga MM, Gil MH, de Sousa HC. Supercritical solvent 2006;36:318–24. impregnation of natural bioactive compounds in N-carboxybutyl chitosan [84] Jayakumar R, Prabaharan M, Sudheesh Kumar PT, Nair SV, Tamura H. membranes for the development of topical wound healing applications. J Biomaterials based on chitin and chitosan in wound dressing applications. Control Release 2010;148:e33–5. Biotechnol Adv 2011;29:322–37. [118] Dai YN, Li P, Zhang JP, Wang AQ, Wei Q. A novel pH sensitive N-succinyl [85] Lee Y, Chang J, Yang M, Chien C, Lai W. Aceleration of wound dressing in chitosan/alginate hydrogel bead for nifedipine delivery. Biopharm Drug diabetic rats by layered hydrogel dressing. Carbohydr Polym Dispos 2008;29:173–84. 2012;88:809–19. [119] Han T, Nwe N, Furuike T, Tokura S, Tamura H. Methods of N-acetylated [86] Meinel A, Germershaus O, Luhmann T, Merkle HP, Meinel L. Electrospun chitosan scaffolds and its in vitro biodegradation by lysozyme. J Biomed Sci matrices for localized drug delievery: current technologies and selected Eng 2012;5:15–23. biomedical applications. Eur J Pharm Biopharm 2012;81:1–13. [120] Chen R, Wang G, Chen C, Ho H, Shen M. Development of a new N-O- [87] Nussinovitch A, Ben-Zion OM. Depolymerized polysaccharide-based hydrogel (carboxymethyl)/chitosan/collagen matrixes as a wound dressing. adhesive and methods of use therefore. US Patent 20110190401 A1; 2011. Biomacromolecules 2006;7:1058–64. [88] Nisbet L. Wound dressing materials. US Patent 20120135062 A1; 2012. [121] Mattioli-Belmonte M, Gigante A, Muzzarelli RAA, Politano R, Benedittis A, [89] Matsumoto Y, Kuroyanagi Y. Development of a wound dressing composed of Specchia N, et al. N-N-dicarboxymethyl chitosan as delivery agent for bone hyaluronic acid sponge containing arginine and epidermal growth factor. J morphogenetic protein in the repair of articular cartilage. Med Biol Eng Biomater Sci Polym Ed 2010;21:715–26. Comput 1999;37:130–4. [90] Hong HJ, Jin SE, Park JS, Ahn WS, Kim CK. Accelerated wound healing by [122] Weng L, Romanov A, Rooney J, Chen W. Non-cytotoxic, in siu gelable smad3 antisense oligonucleotides-impregnated chitosan/alginate hydrogels composed of N-carboxyethyl chitosan and oxidized dextran. polyelectrolyte complex. Biomaterials 2008;29:4831–7. Biomaterials 2008;29:3905–13. [91] Altman AM, Yan Y, Matthias N, Bai X, Rios C, Mathur AB, et al. IAFTS [123] Zhang C, Ping Q, Zhang H, Shen J. Synthesis and characterization of water- collection: human adipose-derived stem cells seeded on a silk fibroin- soluble O-succinyl-chitosan. Eur Polym J 2003;39:1629–34. chitosan scaffold enhance wound repair in a murine soft tissue injury model. [124] Yin L, Fei L, Cui F, Tang C, Yin C. Superporous hydrogels containing Stem Cells 2009;27:250–8. poly(acrylic acid-co-acrylamide)/o-carboxymethyl chitosan interpenetrating [92] Suganya S, Ram TS, Lakshmi BS, Giridev VR. Herbal drug incorporated polymer networks. Biomaterials 2007;28:1258–66. antibacterial nanofibrous mat fabricated by electrospinning: an excellent [125] Berscht PC, Nies B, Liebendorfer A, Kreuter J. Incorporation of basic matrix for wound dressings. J Appl Polym Sci 2011;121:2893–9. fibroblast growth factor into methylpyrrolidinone chitosan fleeces and [93] Zoher K, Kolli ME, Riahi F, Doufnoune R. Preparation and characterization of determination of the in vitro release characteristics. Biomaterials hydrocolloid biopolymer-based films for dressings application. Int J Polym 1994;15:593–600. Mater 2009;58:665–80. [126] Censi R, Di Martino P, Vermonden T, Hennink WE. Hydrogels for protein [94] Zahedi P, Rezaeian I, Ranaei-Siadat S, Jafari S, Supaphol P. A review on wound delivery in tissue engineering. J Control Release 2012;161:680–92. dressings with an emphasis on electrospun nanofibrous polymeric bandages. [127] Azad AK, Sermsintham N, Chandrkrachang S, Stevens WF. Chitosan Polym Adv Technol 2010;21:77–95. membrane as a wound-healing dressing: characterization and clinical [95] Sionkowska A. Current research on the blends of natural and synthetic application. J Biomed Mater Res B Appl Biomater 2004;69:216–22. polymers as new biomaterials: review. Prog Polym Sci 2011;36:1254–76. [128] Kumar MNVR. A review of chitin and chitosan applications. React Funct [96] Muzzarelli RAA, Muzzarelli C. Chitosan chemistry: relevance to the Polym 2000;46:1–27. biomedical sciences. Adv Polym Sci 2005;186:151–209. [129] Saranya N, Moorthi A, Saravanan S, Devi MP, Selvamurugan N. Chitosan and [97] Seetharaman S, Shanmugasundaram N, Stowers RS, Mullens C, Baer DG, Suggs its derivatives for gene delivery. Int J Biol Macromol 2011;48:234–8. LJ, et al. A PEGylated fibrin-based wound dressing with antimicrobial and [130] Bhattarai N, Gunn J, Zhang M. Chitosan-based hydrogels for controlled, angiogenic activity. Acta Biomater 2011;7:2787–96. localized drug delivery. Adv Drug Deliv Rev 2010;62:83–99. [98] Breen AM, Dockery P, O’Brien T, Pandit AS. The use of therapeutic gene eNOS [131] Takei T, Nakahara H, Ijima H, Kawakami K. Synthesis of a chitosan derivative delivered via a fibrin scaffold enhances wound healing in a compromised soluble at neutral pH and gellable by freeze-thawing, and its application in wound model. Biomaterials 2008;29:3143–51. wound care. Acta Biomater 2012;8:686–93. [99] Yang Y, Xia T, Zhi W, Wei L, Weng J, Zhang C, et al. Promotion of skin [132] Muzzarelli RAA. Chitins and chitosans for the repair of wounded skin, nerve, regeneration in diabetic rats by electrospun core-sheath fibers loaded with cartilage and bone. Carbohydr Polym 2009;76:167–82. basic fibroblast growth factor. Biomaterials 2011;32:4243–54. [133] Patterson J, Martino MM, Hubbell JA. Biomimetic materials in tissue [100] Tabata Y. Biomaterial technology for tissue engineering applications. Journal engineering. Mater Today 2010;13:14–22. of the Royal Society Interface 2009:S311–24. [134] Liao YH, Jones SA, Forbes B, Martin GP, Brown MB. Hyaluronan [101] Malafaya PB, Silva GA, Reis RL. Natural-origin polymers as carriers and pharmaceutical characterization and drug delivery. Drug Deliv scaffolds for biomolecules and cell delivery in tissue engineering 2005;12:327–42. applications. Adv Drug Deliv Rev 2007;59:207–33. [135] Price RD, Berry MG, Navsaria HA. Hyaluronic acid: the scientific and clinical [102] Sell SA, Wolfe PS, Garg K, McCool JM, Rodriguez IA, Bowlin GL. The use of evidence. J Plast Reconstr Aesthet Surg 2007;60:1110–9. natural polymers in tissue engineering: a focus on electrospun extracellular [136] Galeano M, Polito F, Bitto A, Irrera N, Campo GM, Avenoso A, et al. Systemic matrix analogues. Polym Adv Technol 2010;2:522–53. administration of high-molecular weight hyaluronan stimulates wound [103] Huang S, Fu X. Naturally derived materials-based cell and drug delivery healing in genetically diabetic mice. Biochim Biophys Acta 2011;1812:752–9. systems in skin regeneration. J Control Release 2010;142:149–59. [137] Xu H, Ma L, Shi H, Gao C, Han C. Chitosan–hyaluronic acid hybrid film as a [104] Tessmar JK, Gopferich AM. Matrices and scaffolds for protein delivery in novel wound dressing: in vitro and in vivo studies. Polym Adv Technol tissue engineering. Adv Drug Deliv Rev 2007;58:274–91. 2007;18:869–75. 7112 L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114

[138] Uppal R, Ramanswamy GN, Arnold C, Goodband R, Wang Y. Hyaluronic acid [169] Kondo S, Niiyama H, Yu A, Kuroyanagi Y. Evaluation of a wound dressing nanofiber wound dressing-production, characterization, and in vivo behavior. composed of hyaluronic acid and collagen sponge containing epidermal J Biomed Mater Res 2011;97B:20–9. growth factor in diabetic mice. Journal of Biomaterials Science Polymer [139] Vazquez JR, Short B, Findlow AH, Nixon BP, Boulton AJM, Armstrong DG. Edition 2011. Outcomes of hyaluronan therapy in diabetic foot wounds. Diabetes Res Clin [170] Lee CR, Grodzinsky AJ, Spector M. The effects of cross-linking of collagen- Pract 2003;59:123–7. glycosaminoglycan scaffolds on compressive stiffness, chondrocyte- [140] Gall Y. Hyaluronic acid: structure, metabolism and implication in mediated contraction, proliferation and biosynthesis. Biomaterials cicatrization. Ann Dermatol Venereol 2010;137(Suppl. 1):S30–9. 2001;22:3145–54. [141] Mano JF, Silva GA, Azevedo HS, Malafaya PB, Sousa RA, Silva SS, et al. Natural [171] Chen ZG, Wang PW, Wei B, Mo XM, Cui FZ. Electrospun collagen-chitosan origin biodegradable systems in tissue engineering and regenerative nanofiber: a biomimetic extracellular matrix for endothelial cell and smooth medicine: present status and some moving trends. J R Soc Interface muscle cell. Acta Biomater 2010;6:372–82. 2007;4:999–1030. [172] Srinivasan A, Sehgal PK. Characterization of biocompatible collagen fibers—a [142] Solway DR, Clark WA, Levinson DJ. A parallel open-label trial to evaluate promising candidate for cardiac patch. Tissue Eng Part C Methods microbial cellulose wound dressing in the treatment of diabetic foot ulcers. 2010;16:895–903. Int Wound J 2011;8:69–73. [173] Zhong SP, Zhang YZ, Lim CT. Tissue scaffolds for skin wound healing and [143] Sannino A, Demitri C, Madaghiele M. Biodegradable cellulose-based dermal reconstruction. Nanomed Nanobiotechnol 2010;2:510–25. hydrogels: design and applications. Materials 2009;2:353–73. [174] Liu X, Ma PX. Phase separation, pore structure, and properties of nanofibrous [144] Helenius G, Backdahl H, Bodin A, Nannmark U, Gatenholm P, Risberg B. In gelatin scaffolds. Biomaterials 2009;30:4094–103. vivo biocompatibility of bacterial cellulose. J Biomed Mater Res Part A [175] Gioffrè M, Torricelli P, Panzavolta S, Rubini K, Bigi A. Role of pH on stability 2006;76A:431–8. and mechanical properties of gelatin films. J Bioact Compat Polym [145] Du J, Hsieh Y. Cellulose/chitosan hybrid nanofibers from electrospinning of 2012;27:67–77. their ester derivatives. Cellulose 2009;16:247–60. [176] Grover CN, Cameron RE, Best SM. Investigating the morphological, [146] Espinoza-Herrera N, Pedrosas-Islas R, Martin-Martinez ES, Cruz-Orea A, mechanical and degradation properties of scaffolds comprising collagen, Tomes SA. Thermal, mechanical and microstructures properties of gelatin and elastin for use in soft tissue engineering. J Mech Behav Biomed cellulose derivatives films: a comparative study. Food Biophys Mater 2012;10:62–74. 2011;6:106–14. [177] Farris S, Song J, Huang Q. Alternative reaction mechanism for the [147] Czaja W, Krystynowicz A, Bielecki S, Brown Jr RM. Microbial cellulose—the cross-linking of gelatin with glutaraldehyde. J Agric Food Chem natural power to heal wounds. Biomaterials 2006;27:145–51. 2010;58:998–1003. [148] Ferreira LM, Sobral CS, Blanes L, Ipolito MZ, Horibe EK. Proliferation of [178] Rujitanaroj P, Pimpha N, Supaphol P. Wound-dressing materials with fibroblasts cultured on a hemi-cellulose dressing. J Plast Reconstr Aesthet antibacterial activity from electrospun gelatin fiber mats containing silver Surg 2009;5:865–9. nanoparticles. Polym Degrad Stab 2008;49:4723–32. [149] Jung K, Kim Y, Kim H, Jin H. Antimicrobial properties of hydrated cellulose [179] Panzavolta S, Gioffré M, Focarete ML, Gualandi C, Foroni L, Bigi A. Electrospun membranes with silver nanoparticles. J Biomater Sci Polym Ed gelatin nanofibers: optimization of genipin cross-linking to preserve fiber 2009;20:311–24. morphology after exposure to water. Acta Biomater 2011;7:1702–9. [150] Serafica G, Mormino R, Oster GA, Lentz KE, Koehler KP. Microbial cellulose [180] Saha N, Saarai A, Roy N, Kitano T, Saha P. Polymeric biomaterial based wound dressing for treating chronic, wounds. US7704523 B2 2010. hydrogels for biomedical applications. J Biomater Nanobiotechnol [151] Cullen MB, Silcock DW, Boyle C. Wound dressing comprising oxidized 2011;2:85–90. cellulose and human recombinat collagen. Patent US 20107833790 B2; 2010. [181] Singh O, Gupta SS, Soni M, Moses S, Shukla S, Mathur RK. Collagen dressing [152] d’Ayala GG, Malinconico M, Laurienzo P. Marine derived polysaccharides for versus conventional dressings in burn and chronic wounds: a retrospective biomedical applications: chemical modification approaches. Molecules study. J Cutan Aesthet Surg 2011;4:12–6. 2008;13:2069–106. [182] Arul V, Masilamoni JG, Jesudason EP, Jaji PJ, Inayathullah M, Dicky John DG, [153] Lee KY, Mooney DJ. Hydrogels for tissue engineering. Chem Rev et al. Glucose oxidase incorporated collagen matrices for dermal wound 2001;101:1869–79. repair in diabetic rat models: a biochemical study. J Biomater Appl [154] Boanini E, Rubini K, Panzavolta S, Bigi A. Chemico-physical characterization 2012;26:917–38. of gelatin films modified with oxidized alginate. Acta Biomater [183] Adhirajan N, Shanmugasundaram N, Shanmuganathan S, Babu M. Collagen- 2010;6:383–8. based wound dressing for doxycycline delivery: in-vivo evaluation in an [155] Jeon O, Powell C, Solorio LD, Krebs MD, Alsberg E. Affinity-based growth infected excisional wound model in rats. J Pharm Pharmacol factor delivery using biodegradable, photocrosslinked heparin-alginate 2009;61:1617–23. hydrogels. J Control Release 2011;154:258–66. [184] Manizate F, Fuller A, Gendics C, Lantis J. A prospective, single-center, [156] Kim JO, Choi JY, Park JK, Kim JH, Jin SG, Chang SW, et al. Development of nonblinded, comparative, postmarket clinical evaluation of a bovine- clindamycin-loaded wound dressing with polyvinyl alcohol and sodium derived collagen with ionic silver dressing versus a alginate. Biol Pharm Bull 2008;31:2277–82. carboxymethylcellulose and ionic silver dressing for the reduction of [157] Han J, Zhou Z, Yin R, Yang D, Nie J. Alginate-chitosan/hydroxyapatite bioburden in variable-etiology, bilateral lower-extremity wounds. Adv Skin polyelectrolyte complex porous scaffolds: preparation and characterization. Wound Care 2012;25:220–5. Int J Biol Macromol 2010;46:199–205. [185] Kawai K, Suzuki S, Tabata Y, Nishimura Y. Accelerated wound healing through [158] Foster AVM, Greenhill MT, Edmonds ME. Comparing two dressings in the the incorporation of basic fibroblast growth factor-impregnated gelatin treatment of diabetic foot ulcers. J Wound Care 1994;3:224–8. microspheres into artificial dermis using a pressure-induced decubitus ulcer [159] Tarun K, Gobi N. Calcium alginate/PVA blended nano fibre matrix for wound model in genetically diabetic mice. Br J Plast Surg 2005;58:1115–23. dressing. Indian J Fibre Text Res 2012;37:127–32. [186] Kanda N, Morimoto N, Ayvazyan AA, Takemoto S, Kawai K, Nakamura Y, et al. [160] Lee CH, Singla A, Lee Y. Biomedical applications of collagen. Int J Pharm Evaluation of a novel collagen-gelatin scaffold for achieving the sustained 2001;221:1–22. release of basic fibroblast growth factor in a diabetic mouse model. J Tissue [161] Valenta C, Auner BG. The use of polymers for dermal and transdermal Eng Regenerative Med 2012. delivery. Eur J Pharm Biopharm 2004;58:279–89. [187] Ahmed TAE, Dare EV, Hincke M. Fibrin: a versatile scaffold for tissue [162] Arul V, Kartha R, Jayakumar R. A therapeutic approach for diabetic wound engineering applications. Tissue Eng Part B 2008;14:199–245. healing using biotinylated GHK incorporated collagen matrices. Life Sci [188] Chen TM, Tsai JC, Burnouf T. A novel technique combining platelet gel, skin 2007;80:275–84. graft, and fibrin glue for healing recalcitrant lower extremity ulcers. Dermatol [163] Parenteau-Bareil R, Gauvin R, Berthod F. Collagen-based biomaterials for Surg 2010;36:453–60. tissue engineering applications. Materials 2010;3:1863–87. [189] Pedroso DC, Tellechea A, Moura L, Fidalgo-Carvalho I, Duarte J, Carvalho E, [164] Cen L, Liu W, Cui L, Zhang W, Cao Y. Collagen tissue engineering: et al. Improved survival, vascular differentiation and wound healing potential development of novel biomaterials and applications. Pediatr Res of stem cells co-cultured with endothelial cells. PLoS ONE 2011;6:1–12. 2008;63:492–6. [190] Hasmann A, Gewessler U, Hulla E, Schneider KP, Binder B, Francesko A, et al. [165] Lammers G, Tjabringa GS, Schalkwijk J, Daamen WF, van Kuppevelt TH. A Sensor materials for the detection of human neutrophil elastase and molecularly defined array based on native fibrillar collagen for the cathepsin G activity in wound fluid. Exp Dermatol 2011;20:508–13. assessment of skin tissue engineering biomaterials. Biomaterials [191] Ruge M. Evaluation of the effect of Vivostat Platelet Rich Fibrin (PRF) in the 2009;30:6213–20. treatment of diabetic foot ulcers. wwwclinicaltrialsgov (last accessed October [166] Antonio F, Guillem R, Sonia T, Clara M, Piergiorgio G, Valeria C, et al. 2012) 2011;NCT00770939. Cross-linked collagen sponges loaded with plant polyphenols with [192] Mandal BB, Kundu SC. Cell proliferation and migration in silk fibroin 3D inhibitory activity towards chronic wound enzymes. Biotechnol J scaffolds. Biomaterials 2009;30:2956–65. 2011;6:1208–18. [193] Inpanya P, Faikrua A, Ounaroon A, Sittichokechaiwut A, Viyoch J. Effects of the [167] Lin Y, Tan F, Marra KC, Jan S, Liu D. Synthesis and characterization of collagen/ blended fibroin/aloe gel film on wound healing in streptozotocin-induced hyaluronan/chitosan composite sponges for potential biomedical diabetic rats. Biomed Mater 2012;7:035008. applications. Acta Biomater 2009;5:2591–600. [194] Dash R, Ghosh SK, Kaplan DL, Kundu SC. Purification and biochemical [168] Zeugolis DI, Paul GR, Attenburrow G. Cross-linking of extruded characterization of a 70 kDa sericin from tropical tasar silkworm, Antheraea collagen fibers—a biomimetic three-dimensional scaffold for tissue mylitta. Comp Biochem Physiol B Biochem Mol Biol 2007;147:129–34. engineering applications. J Biomed Mater Res Part A [195] Baldwin AD, Kiick KL. Polysaccharide-modified synthetic polymeric 2009;89A:895–908. biomaterials. Biopolymers 2010;94:128–40. L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114 7113

[196] Hwang MR, Kim JO, Lee JH, Kim YI, Kim JH, Chang SW, et al. Gentamicin- [226] Yang Y, Xia T, Chen F, Wei W, Liu C, He S, et al. Electrospun fibers with loaded wound dressing with polyvinyl alcohol/dextran hydrogel: gel plasmid bFGF polyplex loadings promote skin wound healing in diabetic rats. characterization and in vivo healing evaluation. AAPS PharmSciTech Mol Pharm 2012;9:48–58. 2010;11:1092–103. [227] Huang Z, Lu M, Zhu G, Gao H, Xie L, Zhang X, et al. Acceleration of diabetic- [197] Sun G, Zhang X, Shen Y, Sebastian R, Dickinson LE, Fox-Talbot K, et al. Dextran wound healing with PEGylated rhaFGF in healing-impaired streptozocin hydrogel scaffolds enhance angiogenic responses and promote complete skin diabetic rats. Wound Repair and Regeneration: Official Publication of the regeneration during burn wound healing. PNAS 2011;108:20976–81. Wound Healing Society [and] the European Tissue Repair Society [198] Parulkar BG, Sobti MK, Pardanani DS. Dextranomer dressing in the treatment 2011;19:633–44. of infected wounds and cutaneous ulcers. J Postgrad Med 1985;31:28–33. [228] Biazar E, Roveimiab Z, Shahhosseini G, Khataminezhad M, Zafari M, Majdi A. [199] Koria P, Yagi H, Kitagawa Y, Megeed Z, Nahmias Y, Sheridan R, et al. Self- Biocompatibility evaluation of a new hydrogel dressing based on assembling elastin-like peptides growth factor chimeric nanoparticles for the polyvinylpyrrolidone/polyethylene glycol. J Biomed Biotechnol treatment of chronic wounds. Proc Natl Acad Sci USA 2011;108:1034–9. 2012;2012:343989. [200] Vasconcelos A, Gomes AC, Cavaco-Paulo A. Novel silk fibroin/elastin wound [229] Choi JS, Leong KW, Yoo HS. In vivo wound healing of diabetic ulcers using dressings. Acta Biomater 2012;8:3049–60. electrospun nanofibers immobilized with human epidermal growth factor [201] Daamen WF, Veerkamp JH, van Hest JC, van Kuppevelt TH. Elastin as a (EGF). Biomaterials 2008;29:587–96. biomaterial for tissue engineering. Biomaterials 2007;28:4378–98. [230] Choi JS, Choi SH, Yoo HS. Coaxial electrospun nanofibers for treatment of [202] Mithieux SM, Rasko JEJ, Weiss ASAS. Synthetic elastin hydrogels derived from diabetic ulcers with binary release of multiple growth factors. J Mater Chem massive elastic assemblies of self-organized human protein monomers. 2011;21:5258–67. Biomaterials 2004;25:4921–7. [231] Himly N, Darwis D, Hardiningsih L. Poly(n-vinylpyrrolidone) hydrogels: [203] Leach JB, Wolinsky JB, Stone PJ, Wong JY. Crosslinked alpha-elastin Hydrogel composites as wound dressing for tropical environment. Radiat biomaterials: towards a processable elastin mimetic scaffold. Acta Biomater Phys Chem 1993;42:911–4. 2005;1:155–64. [232] Lugão AB, Machado LDB, Miranda LF, Alvarez MR, Rosiak JM. Study of wound [204] McHale MK, Setton LA, Chilkoti A. Synthesis and in vitro evaluation of dressing structure and hydration/dehydration properties. Radiat Phys Chem enzymatically cross-linked elastin-like polypeptide gels for cartilaginous 1998;52:319. tissue repair. Tissue Eng Part A 2005;11:1768–79. [233] Lugão AB, Rogero SO, Malmonge SM. Rheological behaviour of irradiated [205] Mithieux SM, Tu Y, Korkmaz E, Braet F, Weiss AS. In situ polymerization of wound dressing poly(vinyl pyrrolidone) hydrogels. Radiat Phys Chem tropoelastin in the absence of chemical cross-linking. Biomaterials 2002;63:543–6. 2009;30:431–5. [234] Li Y, Lee PI. Controlled nitric oxide delivery platform based on S-nitrosothiol [206] Wise SG, Mithieux SM, Weiss AS. Engineered tropoelastin and elastin-based conjugated interpolymer complexes for diabetic wound healing. Mol Pharm biomaterials. Adv Protein Chem Struct Biol 2006;78:1–24. 2010;7:254–66. [207] Bourke SL, Al-Khalili M, Briggs T, Michniak BB, Kohn J, Poole-Warren LA. A [235] Naira LS, Laurencin CT. Biodegradable polymers as biomaterials. Prog Polym photo-crosslinked poly(vinyl alcohol) hydrogel growth factor release vehicle Sci 2007;32:762–98. for wound healing applications. AAPS PharmSci 2003;5:E33. [236] Lee J, Cho Y, Lee J, Kim H, Pyun D, Park M, et al. Preparation of wound dressing [208] Varshney L. Role of natural polysaccharides in radiation formation of PVA– using hydrogel polyurethane foam. Trends Biomater Artif Organs hydrogel wound dressing. Nucl Instrum Methods Phys Res Sect B 2001;15:4–6. 2007;255:343–9. [237] Chen Z, Lu H. Constructing sacrificial bonds and hidden lengths for ductile [209] Kim JO, Park JK, Kim JH, Jin SG, Yong CS, Li DX, et al. Development of polyvinyl graphene/polyurethane elastomers with improved strength and toughness. J alcohol-sodium alginate gel-matrix-based wound dressing system Mater Chem 2012;22:12479–90. containing nitrofurazone. Int J Pharm 2008;359:79–86. [238] Varma AK, Bal A, Kumar H, Kesav R, Nair S. Efficacy of polyurethane foam [210] Xia C, Xiao C. Preparation and characterization of dual responsive dressing in debrided diabetic lower limb wounds. Wounds 2008;12:5–8. sodium alginate-g-poly(vinyl alcohol) hydrogel. J Appl Polym Sci 2012;123: [239] Shi R, Chen D, Liu Q, Wu Y, Xu X, Zhang L, et al. Recent advances in synthetic 2244–9. bioelastomers. Int J Mol Sci 2009;10:4223–56. [211] de Souza Costa-Junior E, Pereira MM, Mansur HS. Properties and [240] Khil MS, Cha DI, Kim HY, Kim IS, Bhattarai N. Electrospun nanofibrous biocompatibility of chitosan films modified by blending with PVA and polyurethane membrane as wound dressing. J Biomed Mater Res B Appl chemically crosslinked. Journal of Materials Science Materials in Medicine Biomater 2003;67:675–9. 2009;20:553–61. [241] Davis FJ, Mitchell GR. Polyurethane based materials with application in [212] Linh NTB, Min YK, Song H, Lee B. Fabrication of polyvinyl alcohol/gelatin medical devices. Biomater Prototyping Appl Med 2008;3:27–48. nanofiber composites and evaluation of their material properties. J Biomed [242] Shah CB, Swaniker B, Dowd BJ, Brandon B. Efficacy and mode of action of a Mater Res Part B 2010;95B:184–91. new PHMB impregnated polyurethane foam dressing. Covidien 2009;10:1–8. [213] Fathi E, Atyabi N, Imani M, Alinejad Z. Physically crosslinked polyvinyl [243] Barrett S. Mepilex Ag: an antimicrobial, absorbent foam dressing with Safetac alcohol-dextran blend xerogels: morphology and thermal behavior. technology. Br J Nurs 2009;18:S28–36. Carbohydr Polym 2011;84:145–52. [244] Radhakumary C, Nandkumar AM, Nair PD. Hyaluronic acid-g-poly(HEMA) [214] Drury JL, Mooney DJ. Hydrogels for tissue engineering: scaffold design copolymer with potential implications for lung tissue engineering. Carbohydr variables and applications. Biomaterials 2003;24:4337–51. Polym 2011;85:439–45. [215] Masters KS, Leibovich SJ, Belem P, West JL, Poole-Warren LA. Effects of nitric [245] Tsou T, Tang S, Huang Y, Wu J, Young J, Wang H. Poly(2-hydroxyethyl oxide releasing poly(vinyl alcohol) hydrogel dressings on dermal wound methacrylate) wound dressing containing ciprofloxacin and its drug release healing in diabetic mice. Wound Repair and Regeneration: Official studies. J Mater Sci Mater Med 2005;16:95–100. Publication of the Wound Healing Society [and] the European Tissue Repair [246] Halpenny GM, Steinhardt RC, Okialda KA, Mascharak PK. Characterization of Society 2002;10:286–94. pHEMA-based hydrogels that exhibit light-induced bactericidal effect via [216] Manju S, Antony M, Sreenivasan K. Synthesis and evaluation of a hydrogel release of NO. J Mater Sci Mater Med 2009;20:2353–60. that binds glucose and releases ciprofloxacin. J Mater Sci 2010;45:4006–12. [247] Rayment EA, Dargaville T, Upton Z. Wound repair composition and method. [217] Zhu J. Biactive modification of poly(ethylene glycol) hydrogels for tissue Patent 20100172860 2010. engineering. Biomaterials 2010;31:4639–56. [248] Wang D, Song YP, Lin L, Wang X, Wang Y. A novel phosphorus-containing [218] Gibas I, Janik H. Review: synthetic polymer hydrogels for biomedical poly(lactic acid) toward its flame retardation. Polymer 2011;52:233–8. applications. Chem Chem Technol 2010;4:297–304. [249] Ignatova M, Manolova N, Markova N, Rashkov I. Electrospun non-woven [219] Peppas NA, Keys KB, Torres-Lugo M, Lowman AM. Poly(ethylene glycol)- nanofibrous hybrid mats based on chitosan and PLA for wound-dressing containing hydrogels in drug delivery. J Controlled Release 1999;62:81–7. applications. Macromol Biosci 2009;9:102–11. [220] Beamish JA, Zhu J, Kottke-Marchant K, Marchant RE. The effects of [250] Armentano I, Dottori M, Fortunati E, Mattioli S, Kenny JM. Biodegradable monoacrylated poly(ethylene glycol) on the properties of poly(ethylene polymer matrix nanocomposites for tissue engineering: a review. Polym glycol) diacrylate hydrogels used for tissue engineering. J Biomed Mater Res Degrad Stab 2010;95:2126–46. Part A 2010;92:441–50. [251] Li S. Hydrolytic degradation characteristics of aliphatic polyesters derived [221] Metters A, Hubbell J. Network formation and degradation behavior of from lactic and glycolic acids. J Biomed Mater Res Part B Appl Biomater hydrogels formed by Michael-type addition reactions. Biomacromolecules 1999;48:342–53. 2005;6:290–301. [252] Dong X, Xu J, Wang W, Luo H, Liang X, Zhang L, et al. Repair effect of diabetic [222] Sanborn TJ, Messersmith PB, Barron AE. In situ crosslinking of a biomimetic ulcers with recombinant human epidermal growth factor loaded by peptide-PEG hydrogel via thermally triggered activation of factor XIII. sustained-release microspheres. Sci China C Life Sci 2008;51:1039–44. Biomaterials 2002;23:2703–10. [253] Chu Y, Yu D, Wang P, Xu J, Li D, Ding M. Nanotechnology promotes the full- [223] Sun G, Zhang X, Chu C. Effect of molecular weight of polyethylene glycol thickness diabetic wound healing effect of recombinant human epidermal (PEG) on the properties of chitosan-PEG-poly (N-isopropylacrymide) growth factor in diabetic rats. Wound Repair and Regeneration: Official hydrogels. J Mater Sci Mater Med 2008;19:2865–72. Publication of the Wound Healing Society [and] the European Tissue Repair [224] Sokolsky-Papkov M, Agashi K, Olaye A, Shakesheff K, Domb AJ. Polymer Society 2010;18:499–505. carriers for drug delivery in tissue engineering. Adv Drug Deliv [254] Xu X, Zhong W, Zhou S, Trajtman A, Alfa M. Electrospun PEG–PLA nanofibrous 2007;59:187–209. membrane for sustained release of hydrophilic antibiotics. J Appl Polym Sci [225] Lee PY, Cobain E, Huard J, Huang L. Thermosensitive hydrogel PEG-PLGA-PEG 2010;118:588–95. enhances engraftment of muscle-derived stem cells and promotes healing in [255] Merrel JG, McLaughlin SW, Tie L, Laurencin CT, Chen AF, Nair LS. Curcumin- diabetic wound. Mol Ther 2007;15:1189–94. loaded poly(e-caprolactone) nanofibres: diabetic wound dressing with anti- 7114 L.I.F. Moura et al. / Acta Biomaterialia 9 (2013) 7093–7114

oxidant and anti-inflammatory properties. Clin Exp Pharmacol Physiol [278] Ponrasu T, Suguna L. Efficacy of Annona squamosa on wound healing in 2009;36:1149–56. streptozotocin-induced diabetic rats. Int Wound J 2012;9:613–23. [256] Kang X, Xie Y, Powell HM, James Lee L, Belury MA, Lannutti JJ, et al. [279] Jacobi J, Jang JJ, Sundram U, Dayoub H, Fajardo LF, Cooke JP. Nicotine Adipogenesis of murine embryonic stem cells in a three-dimensional accelerates angiogenesis and wound healing in genetically diabetic mice. Am culture system using electrospun polymer scaffolds. Biomaterials J Pathol 2002;161:97–104. 2007;28:450–8. [280] Bitto A, Minutoli L, Altavilla D, Polito F, Fiumara T, Marini H, et al. Simvastatin [257] Galiano RD, Tepper OM, Pelo CR, Bhatt KA, Callaghan M, Bastidas N, et al. enhances VEGF production and ameliorates impaired wound healing in Topical vascular endothelial growth factor accelerates diabetic wound experimental diabetes. Pharmacol Res 2008;57:159–69. healing through increased angiogenesis and by mobilizing and recruiting [281] Bagheri M, Jahromi BM, Mirkhani H, Solhjou Z, Noorafshan A, Zamani A, et al. bone marrow-derived cells. Am J Pathol 2004;164:1935–47. Azelnidipine, a new calcium channel blocker, promotes skin wound healing [258] Li H, Fu X, Zhang L, Huang Q, Wu Z, Sun T. Research of PDGF-BB gel on the in diabetic rats. J Surg Res 2011;169:e101–7. wound healing of diabetic rats and its pharmacodynamics. J Surg Res [282] Ko SH, Nauta A, Morrison SD, Zhou H, Zimmermann A, Gurtner GC, et al. 2008;145:41–8. Antimycotic ciclopirox olamine in the diabetic environment promotes [259] Uchi H, Igarashi A, Urabek Koga T,, Nakayama J, Kawamori R, et al. Clinical angiogenesis and enhances wound healing. PLoS ONE 2011;6:e27844. efficacy of basic fibroblast growth factor (bFGF) for diabetic ulcer. Eur J [283] McLaughlin PJ, Pothering CA, Immonen JA, Zagon IS. Topical treatment with Dermatol 2009;19:461–8. the opioid antagonist naltrexone facilitates closure of full-thickness wounds [260] Gallagher KA, Liu ZJ, Xiao M, Chen H, Goldstein LJ, Buerk DG, et al. Diabetic in diabetic rats. Exp Biol Med 2011;236:1122–32. impairments in NO-mediated endothelial progenitor cell mobilization and [284] Wang W, Lin S, Xiao Y, Huang Y, Tan Y, Cai L, et al. Acceleration of diabetic homing are reversed by hyperoxia and SDF-1 alpha. J Clin Invest wound healing with chitosan-crosslinked collagen sponge containing 2007;117:1249–59. recombinant human acidic fibroblast growth factor in healing-impaired STZ [261] Kwon DS, Gao X, Liu YB, Dulchavsky DS, Danyluk AL, Bansal M, et al. diabetic rats. Life Sci 2008;82:190–204. Treatment with bone marrow-derived stromal cells accelerates wound [285] Ben-shalom N, Zvi N, Abraham P, Dror R. Novel injectable chitosan mixtures healing in diabetic rats. Int Wound J 2008;5:453–63. forming hydrogels. EP2121026 2009. [262] Barcelos LS, Duplaa C, Krankel N, Graiani G, Invernici G, Katare R, et al. [286] Zhang H, Qadeer A, Chen W. In situ gelable interpenetrating double network Human CD133+ progenitor cells promote the healing of diabetic ischemic hydrogel formulated from binary components: thiolated chitosan and ulcers by paracrine stimulation of angiogenesis and activation of Wnt oxidized dextran. Biomacromolecules 2011;12:1428–37. signaling. Circ Res 2009;104:1095–102. [287] Lobmann R, Pittasch D, Muhlen I, Lehnert H. Autologous human keratinocytes [263] Amos PJ, Kapur SK, Stapor PC, Shang H, Bekiranov S, Khurgel M, et al. Human cultured on membranes composed of benzyl ester of hyaluronic acid for adipose-derived stromal cells accelerate diabetic wound healing: impact of grafting in nonhealing diabetic foot lesions: a pilot study. J Diabetes cell formulation and delivery. Tissue Eng Part A 2010;16:1595–606. Complications 2003;17:199–204. [264] Lee KB, Choi J, Cho SB, Chung JY, Moon ES, Kim NS, et al. Topical embryonic [288] Scherer SS, Pietramaggiori G, Matthews J, Perry S, Assmann A, Carothers A, stem cells enhance wound healing in diabetic rats. J Orthop Res et al. Poly-N-acetyl glucosamine nanofibers: a new bioactive material to 2011;29:1554–62. enhance diabetic wound healing by cell migration and angiogenesis. Ann [265] Asai J, Takenaka H, Ii M, Asahi M, Kishimoto S, Katoh N, et al. Topical Surg 2009;250:322–30. application of ex vivo expanded endothelial progenitor cells promotes [289] Sobotka L, Smahelova A, Pastorova J, Kusalova M. A case report of the vascularisation and wound healing in diabetic mice. Int Wound J 2012. treatment of diabetic foot ulcers using a sodium hyaluronate and iodine [266] Keswani SG, Katz AB, Lim FY, Zoltick P, Radu A, Alaee D, et al. Adenoviral complex. Int J Low Extrem Wounds 2007;6:143–7. mediated gene transfer of PDGF-B enhances wound healing in type I and type [290] Pietramaggiori G, Yang H, Scherer SS, Kaipainen A, Chan R, Alperovich MBS, II diabetic wounds. Wound Repair Regen 2004;12:497–504. et al. Effects of poly-N-acetyl glucosamine (pGlcNAc) patch on wound healing [267] Badillo AT, Chung S, Zhang L, Zoltick P, Liechty KW. Lentiviral gene transfer of in db/db Mouse. J Trauma Acute Care Surg 2008;64:803–8. SDF-1alpha to wounds improves diabetic wound healing. J Surg Res [291] Bayaty F, Abdulla M, Hassan MIA, Masud M. Wound healing potential by 2007;143:35–42. hyaluronate gel in streptozotocin-induced diabetic rats. Sci Res Essays [268] Mohebali K, Ro P, Young DM, Boudreau N, Hansen SL. Transfer of Hox B3 2010;5:2756–60. gene accerelates wound healing in diabetic mice. J Am Coll Surg [292] Abbruzzese L, Rizzo L, Fanelli G, Tedeschi A, Scatena A, Goretti C, et al. A 2008;207:S58. Effectiveness and safety of a novel gel dressing in the management of [269] Cheng CF, Sahu D, Tsen F, Zhao Z, Fan J, Kim R, et al. A fragment of neuropathic leg ulcers in diabetic patients: a prospective double-blind secreted Hsp90alpha carries properties that enable it to accelerate randomized trial. Int J Low Extrem Wounds 2009;8:134–40. effectively both acute and diabetic wound healing in mice. J Clin Invest [293] Lazaro-Martinez JL, Aragon-Sanchez JV, Garcia-Morales E, Beneit- 2011;121:4348–61. Montesinos JV, Gonzalez-Jurado M. A retrospective analysis of the cost- [270] Gibran NS, Jang YC, Isik FF, Greenhalgh DG, Muffley LA, Underwood RA, et al. effectiveness of a collagen/oxidized regenerated cellulose dressing in the Diminished neuropeptide levels contribute to the impaired cutaneous treatment of neuropathic diabetic foot ulcers. Ostomy/Wound Manage healing response associated with diabetes mellitus. J Surg Res 2002;108: 2010;56:4–8. 122–8. [294] Ulrich D, Smeets R, Unglaub F, Woltje M, Pallua N. Effect of oxidized [271] Scott JR, Tamura RN, Muangman P, Isik FF, Xie C, Gibran NS. Topical substance regenerated cellulose/collagen matrix on proteases in wound exudate of P increases inflammatory cell density in genetically diabetic murine wounds. patients with diabetic foot ulcers. J Wound Ostomy and Continence Nurs Wound Repair Regen 2008;16:529–33. 2011;38:522–8. [272] Hamed S, Ullmann Y, Masoud M, Hellou E, Khamaysi Z, Teot L. Topical [295] Choi DS, Kim S, Lim Y, Gwon H. Hydrogel incorporated with chestnut honey erythropoietin promotes wound repair in diabetic rats. J Invest Dermatol accelerates wound healing and promotes early HO-1 protein expression in 2010;130:287–94. diabetic (db/db) mice. Tissue Eng Regenerat Med 2012;9:36–42. [273] Apikoglu-Rabus S, Izzettin FV, Turan P, Ercan F. Effect of topical insulin on [296] Shaw J, Hughes CM, Lagan KM, Stevenson MR, Irwin CR, Bell PM. The effect of cutaneous wound healing in rats with or without acute diabetes. Clin Exp topical phenytoin on healing in diabetic foot ulcers: a randomized controlled Dermatol 2010;35:180–5. trial. Diabet Med 2011;28:1154–7. [274] Fujita N, Sagaguchi I, Kobayashi H, Ikeda N, Kato Y, Minamino M. An extract [297] Molan P. Honey based wound dressings. USRE42755 E 2011. of the root of Lithospermun erythrorhison accelerates wound healing in [298] Iorio ML, Goldstein J, Adams M, Steinberg J, Attinger C. Functional limb diabetic mice. Biol Pharm Bull 2003;26:329–35. salvage in the diabetic patient: the use of a collagen bilayer matrix and risk [275] Lau TW, Lam FF, Lau KM, Chan YW, Lee KM, Sahota DS, et al. Pharmacological factors for amputation. Plast Reconstr Surg 2011;127:260–7. investigation on the wound healing effects of Radix rehmanniae in an animal [299] Jorgensen B, Karlsmark T, Vogensen H, Haase L, Lundquist R. A pilot study to model of diabetic foot ulcer. J Ethnopharmacol 2009;123:155–62. evaluate the safety and clinical performance of Leucopatch, an autologous, [276] Abu-Al-Basal MA. Healing potential of Rosmarinus officinalis L. on full- additive-free, platelet-rich fibrin for the treatment of recalcitrant chronic thickness excision cutaneous wounds in alloxan-induced-diabetic BALB/c wounds. Int J Low Extrem Wounds 2011;10:218–23. mice. J Ethnopharmacol 2010;131:443–50. [277] Dwivedi VK, Chaudhary M. Comparative wound healing efficacy of ampucare and becaplermin in diabetic rat. Afr J Pharm Pharmacol 2012;6:883–92.